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THE  LIBRARIES 
COLUMBIA  UNIVERSITY 


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Digitized  by  tine  Internet  Arciiive 

in  2010  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/lecturenotesonph13jane 


LECTURE  NOTES  ON 
PHYSIOLOGY 


BY 
HENRY  H.  JANEWAY,  M.D. 


DIGESTION 


NEW    YORK 

PAUL   B.  HOEBER 

67-69  EAST  59th  STREET 


Copyright,  1915 
By  PAUL  B.  HOEBER 


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CO 

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DIGESTION 

The  Meaning  of  Digestion  —  Animal  bodies  can  only 
utilize  as  food  the  three  classes  of  complex  substances 
which  constitute  their  own  tissues.  These  substances  are 
carbohydrates,  fats  and  proteins.  The  animal  body  can 
only  obtain  them  by  eating  them  in  the  form  in  which  they 
exist  in  other  animal  bodies  or  as  they  are  prepared  by 
plant  life.  Moreover,  the  body  can  absorb  and  utilize 
after  absorption,  only  a  few  of  the  many  carbohydrates 
and  fats. 

All  the  proteins  and  practically  all  the  fats  and  carbo- 
hydrates must  be  taken  apart  into  the  simpler  groups  of 
atoms  of  which  they  are  composed  in  order  that  the  groups 
may  first  be  absorbed,  and  that  secondly  from  these 
groups  there  may  be  built  up  again  the  special  kind  of 
proteins,  carbohydrates  and  fats  which  form  the  various 
cells  in  the  human  body. 

The  process  of  taking  the  carbohydrates,  fats  and  pro- 
teins apart  is  called  digestion. 

The  Active  Agents  of  Digestion  —  Special  cells  are 
set  apart  for  fcjrming  these  agents  in  the  human  body. 
They  compose  the  salivary  glands,  the  glands  of  the 
stomach  and  intestine,  and  the  pancreas  and  li\er.  The 
"  taking  apart  "  process  is  accom])lished  by  ferments 
manufactured  by  the  cells  of  these  organs. 

In    the    process    of    absorption    many    of    these    split 

2 


DIGESTION 

products  reunite  only  to  be  taken  apart  and  recombined 
again  in  the  tissues. 

The  Chemical  Nature  of  Digestion  —  Every  disin- 
tegrative change  of  the  kind  of  which  we  are  speaking  is 
accompHshed  by  ferments,  and  is  ahvays  hydrolytic. 

The  more  complex  substances  take  up  a  molecule  of 
water  and  split  in  into  simpler  clearage  products. 

For  each  substance  a  special  ferment  is  necessary. 
Hence  there  is  a  great  multitude  of  ferments. 

The  End  Products  of  Digestion  or  the  Primary 
Chemical  Units  of  the  Body  —  The  end  products  pro- 
duced by  the  digestive  ferments,  those  splitting  the  food 
stuffs  into  compounds  from  which  the  body  can  recon- 
struct its  own  tissues,  are  not  very  numerous. 

Of  the  carbohydrates  they  are  the  monosaccharides  — 
glucose,  fructose  or  levulose,  and  galactose  and  mannose. 

Of  the  fats  they  are  fatty  acids,  or,  in  alkaline  medium, 
soap,  and  glycerine. 

Of  the  proteins  they  are :  — 

THE  AMINO  ACIDS. 


Monobasic  acids  of  fatty 
series  


IT.     Dibasic  acids 


-I.  Glycine  (amino  acetic  acid). 

2.  Alanine  (amino  proprionic  acid). 

3.  Serine  (oxyalanine). 

4.  Amino   (valerianic  acid). 

5.  Leucine  (aminoisobutylacetic  acid). 

6.  Isoleucine   (amino  caproic  acid). 

1.  Aspartic    acid     ("a"    amino    suc- 
cinic acid). 

2.  Glutamic  acid  ("  a  "  amino  glutaric 
acid). 


TTT      15  1     •     !-•  fi-  Phenylalanine. 

III.     Ijenzene  derivatives   ...-<       „        .        ,  ,        ... 

1^2.    tyrosine    (oxyphenylalamne). 

4 


DIGESTION 


TV.     Heterocyclic   Com- 
pounds     


V.     The  Hexone  bases 


VI.     Other  Bodies 


Proline  (pyrrolidine  carboxylic 
acid). 

Oxyproline  (oxypyrrolidine  car- 
boxylic acid). 

Tryptophane  (indolamino  propri- 
ome  acid). 

Lysine   (diamine  caproic  acid). 
Arginine     (guanidinamino     valeri- 
anic acid). 
Histidine. 

Diaminotrioxydodecoic  acid  (a  12 
carbon  atom  compound). 

Cystine  (a  sulphur-containing 
body)  from  aminothio  propionic 
acid. 


The  first  steps  in  digestion  are  performed  within  the 
mouth,  although  the  process  proceeds  only  to  such  a 
shght  extent  in  this  cavity  that  it  may  scarcely  be  said  to 
begin  here. 

The  Three  Salivary  Glands  and  Their  Ducts  — 
Opening  into  the  mouth  are  the  ducts  of  the  three  pairs 
of  salivary  glands.  The  parotid  gland  surrounds  the 
anterior  and  lower  walls  of  the  external  auditory  meatus 
and  empties  by  a  long  duct,  Steno's  duct,  internal  to  the 
buccinator  muscle. 

The  submaxillary  gland  is  situated  beneath  the  body 
of  the  lower  jaw.  Its  duct,  Wharton's  duct,  opens  into 
the  floor  of  the  mouth  at  the  side  of  the  frsenum  of  the 
tongue.  The  sublingual  gland  is  situated  beneath  the 
mucous  membrane  of  the  mouth,  posterior  to  the  sym- 
physis of  the  lower  jaw. 

Its  duct,  the  duct  of  Rivini,  opens  by  the  same  papilla 
as  Wharton's  duct.     When  food  is  taken  into  the  mouth 

6 


DIGESTION 

and  chewed  these  glands  pour  forth  their  secretion  called 
saliva.  In  addition  to  these  glands  the  whole  floor  of  the 
mouth  is  beset  with  numerous  small  glands  which  add  to 
the  secretion  of  the  oral  cavity. 

Physical  Characters  of  Saliva  —  Saliva  possesses  the 
following  physical  characters  — 

1.  Its  specific  gravity  varies  1002  to  1008. 

2.  It  is  a  cloudy  slimy  fluid. 

3.  It  contains  floating  in  it  epithelial  cells,  pus  cells 
and  strings  of  mucus. 

4.  It  is  alkaline  in  reaction. 

Constituents  of  Saliva  —  Its  important  constituents 
are : 

1.  Coagulable  proteins; 

2.  Mucin; 

3.  Ptyalin,  a  diastatic  ferment; 

4.  Potassium  sulphocyanate ; 

The  organic  solids  amount  to  .1   to       .4  per  cent. 

The  inorganic  solids  .4  to       .6  per  cent. 

The  potassium  sulphocyanate    .01   to  .010  per  cent. 

The  body  excretes  the  very  poisonous  cyanides  in  the 
form  of  the  harmless  sulphocyanates  by  the  saliva,  the 
gastric  juice  and  the  kidneys. 

Functions  of  the  Saliva  —  The  most  important  func- 
tion of  the  saliva  is  to  soften  and  moisten  the  food. 

In  virtue  of  the  mucin  which  it  contains  it  makes  the 
food  slippery  so  that  it  is  easily  swallowed. 

In  man  and  some  herbivora  it  performs  a  digestive 
function  upon  starch. 

The  Digestive  Action  of  Saliva  and  the  Resulting 
Products  —  Starch  dissolved  in  water  forms  an  opales- 

8 


DIGESTION 

cent  solution  and  gives  a  blue  color  when  treated  with 
iodine.  Saliva  first  transforms  the  opalescent  solution 
into  a  clear  solution  still  giving  the  blue  color  with  iodine. 
The  starch  has  been  transformed  into  soluble  starch. 
After  a  longer  action  of  the  saliva  the  starch  will  have 
entirely  disappeared  and  the  solution  now  gives  a  red  color 
on  treatment  with  iodine.  The  soluble  starch  has  been 
transformed  into  erthrodextrin  and  maltose. 

Maltose  is  a  sugar  and  hence  its  solution  will  reduce 
Fehling's  solution. 

Later  still  the  addition  of  iodine  to  the  solution  will 
produce  no  change  in  color.  The  erthrodextrin  has  been 
transformed  into  achrodextrin  and  maltose.  Part  of  the 
achrodextrin,  but  never  all,  is  transformed  into  more 
maltose.  In  this  process  of  breaking  up  of  the  huge 
starch  molecule  into  achrodextrin  and  maltose,  other  com- 
pounds, which  we  cannot  detect,  are  doubtless  formed. 

The  Active  Agent  in  Salivary  Digestion  and  the 
Conditions  of  its  Activity  —  The  agent  which  accom- 
plishes this  change  in  the  starch  is  the  ptyalin.  It  acts 
best  at  the  body  temperature  but  will  exhibit  a  feeble 
action  at  o°  C.  and  is  destroyed  at  60°  C.  It  is  most 
active  in  a  neutral  medium,  but  is  rapidly  destroyed  in 
the  presence  of  minute  traces  of  mineral  acids,  even  .003 
per  cent,  hydrochloric  acid.  As  saliva  is  alkaline,  the 
addition  of  a  little  acid  to  saliva  will  increase  its  activity. 

Inasmuch  as  the  food  remains  only  a  short  time  in  the 
mouth  very  little  digestion  takes  places  here,  but  as  the 
saliva  assists  in  the  formation  of  the  bolus  of  food,  and 
coats  the  same  with  mucus,  much  salivarv  digestion  is 


TO 


DIGESTION 

continued  (30  to  40  min.)  in  the  stomach;  first  because  an 
appreciable  time  is  needed  for  sufficient  gastric  juice  to  be 
secreted  to  inhibit  its  action  and  second  because  much  of 
the  ptyaHn  is  protected  in  the  interior  of  masses  of  food 
which  have  been  swallowed. 

The  Histological  Differences  between  the  Various 
Salivary  Glands  —  According  to  the  secretion  produced 
three  kinds  of  salivary  glands  are  recognized;  the  serous 
and  mucous  and  mixed  glands. 

The  cells  of  the  serous  salivary  gland  are  small  gran- 
ular cells  with  a  w^ell  staining  nucleus  and  line  alveoli 
possessing  a  well  marked  lumen.  The  duct  is  lined  with 
columnar  cells.  They  produce  a' serous  secretion.  The 
cells  of  the  mucous  gland  are  larger  and  distended  with 
mucinogen  which  becomes  mucin  after  secretion.  The 
cells  therefore  present  large  clear  spaces  within  them. 
The  ducts  are  short  and  the  alveoli  are  wide.  The  third 
type  may  be  called  a  mixed  type.  The  majority  of  the 
alveoli  are  mucous  in  character.  At  their  ends  are  cres- 
centic-shaped  cells  between  the  mucin  producing  cells. 
They  are  called  demilunar  cells,  they  secrete  a  serous  se- 
cretion. 

The  parotid  gland  is  a  serous  gland,  the  submaxillary 
and  sublingual  glands  are  mixed  glands.  We  must  turn 
to  the  dog  for  an  example  of  a  pure  mucous  salivary 
gland.  The  dog  possesses  a  salivary  gland  in  the  orbit. 
It  is  called  the  orbital  salivary  gland.  It  is  a  pure  mucous 
salivary  gland. 

The  Control  of  the  Secreting  Activity  of  the  Sali- 
vary Glands  by  the  Nervous  System  —  The  salivary 
glands  are  stimulated  to  pour  forth  their  secretion  by  im- 

12 


DIGESTION 

pulses  descending  two  sets  of  nerves  which  enter  the 
glands.  These  impulses  come  from  the  central  nervous 
system  and  are  inaugurated  there  by  other  impulses  pass- 
ing up  to  the  central  nervous  system  along  nerves  having 
their  peripheral  distribution  in  the  tongue  and  mouth. 
Various  kinds  of  stimuli  will  inaugurate  the  impulses  in 
the  central  nervous  system.  If  the  duct  of  a  salivary 
gland  is  implanted  in  the  skin  and  food  is  placed  into  the 
mouth  immediately,  i.e.,  after  two  or  three  seconds,  saliva 
will  begin  to  flow.  Meat  will  cause  less  secretion  than 
starchy  food  but  dry  meat  more  flow  than  moist  meat. 
The  mere  sight  of  food  to  a  hungry  animal  will  be  suffi- 
cient to  excite  the  secretion. 

Amount  of  Saliva  Secreted  —  The  amount  of  saliva 
secreted  is  enormous  in  proportion  to  the  size  of  these 
glands.  In  one  day  each  gland  may  secrete  ten  to  twelve 
times  its  own  weight.  In  twenty-four  hours  the  human 
salivary  glands  may  secrete  a  liter  of  saliva.  In  the  horse 
500  grams  of  hay  may  cause  the  glands  to  produce  one 
liter  of  saliva  and  many  liters  are  produced  in  twenty-four 
hours. 

The  Afferent  and  Efferent  Nerves  of  the  Salivary 
Glands  —  The  nerves  carrying  the  impulses  from  the 
mouth  to  the  brain  are  the  fifth  and  ninth  cranial 
nerves.  The  impulses  to  the  gland  pass  down  two 
sets  of  nerves.  One  set  belongs  to  the  cerebro  spinal 
nerves  and  descends  through  the  seventh  nerve.  This 
set  leaves  the  brain  through  the  nerve  of  Wrisberg, 
then  passes  as  the  chorda  tympani  to  the  lingual  nerve  and 
as  part  of  the  latter  it  reaches  the  neighborhood  of  the 
submaxillary  gland.     It  leaves  the  lingual  nerve  to  join 

14 


DIGESTION  - 

the  submaxillary  ganglion  from  which  its  fibers  are  dis- 
tributed to  the  submaxillary  and  sublingual  gland. 

The  cranial  nerve  supply  to  the  parotid  gland  leaves  the 
brain  in  the  ninth  nerve.  It  leaves  the  ninth  nerve  as 
its  tympanic  branch  or  Jacobson's  nerve. 

Through  Jacobson's  canal  it  enters  the  middle  ear  or 
the  tympanum.  It  leaves  the  tympanum  to  form  the 
vidian  nerve,  passing  with  this  nerve  to  the  otic  ganglion. 
From  this  ganglion  it  joins  the  auriculo  temporal  nerve 
from  which  its  branches  pass  to  the  parotid  gland. 

The  second  set  of  nerves  passing  to  the  salivary  glands 
belong  to  the  sympathetic  nerves.  They  leave  the  spinal 
cord  by  the  anterior  branches  of  the  upper  three  dorsal 
nerves,  pass  to  the  ansa  Vieussens  and  from  this  ring  to 
the  inferior  then  the  superior  ganglion  of  the  sympa- 
thetic. The  peripheral  cell  station  of  these  nerves  is  in 
the  superior  cervical  sympathetic  ganglion  from  which 
post  ganglionic  fibers  pass  to  the  gland. 

The  Effects  Produced  by  Impulses  along  these  Two 
Sets  of  Nerves  and  the  Method  by  which  the  Effects 
are  Investigated  —  What  effect  upon  the  gland  do  the 
impulses  passing  along  these  two  sets  of  fibers  produce? 
We  can  ascertain  the  effect  only  by  electrical  stimulation 
of  the  two  sets  of  nerves. 

The  Cranial  JSferve  Supply  —  Within  two  or  three 
seconds  after  stimulation  of  the  chorda  tympani  there  will 
be  a  wide  dilatation  of  the  arterioles,  capillaries  and  ven- 
ules of  the  submaxillary  gland. 

The  dilatation  will  be  so  extreme  that  arterial  blood 
will  emerge  through  the  veins  coming  from  the  gland  and 
the  little  venules  will  show  a  pulsation.     Accompanying 

i6 


DIGESTION 

this  increased  blood  supply  there  will  be  copious  secretion 
of  saliva  by  the  gland.  Examination  of  the  secretion 
poured  forth  will  show  that  not  only  is  there  an  increase 
of  the  quantit)^  of  fluid  produced  but  also  of  the  per- 
centage of  organic  and  inorganic  solids  contained  in  the 
fluid. 

The  same  effect  is  produced  by  stimulating  the  cranial 
supply  of  the  parotid  gland.  If,  however,  a  dose  of  atro- 
pine is  administered,  stimulation  of  the  chorda  tympani 
will  produce  the  same  vascular  dilatation  in  the  gland  but 
there  will  be  no  increased  secretion  of  saliva. 

In  explanation  of  this  effect  two  possibilities  are  open. 
Either  the  increased  secretion  is  the  result  of  the  improved 
blood  supply  to  the  gland,  caused  by  the  vascular  dilata- 
tion, or,  through  direct  connection  of  the  nerve  fibers 
with  the  secreting  cells,  the  impulses  stimulate  these 
cells  directly. 

The  effects  of  atropine  would  indicate  that  the  second 
hypothesis  was  the  correct  one  because  after  its  adminis- 
tration there  is  no  increased  secretion  although  vascular 
dilatation  is  present.  On  the  other  hand,  if  the  increased 
blood  supply  is  prevented  by  clamping  the  carotid  artery, 
.or  by  bleeding  the  animal,  stimulation  of  the  chorda  tym- 
pani will  be  powerless  to  cause  increase  in  the  quantity 
of  saliva  secreted.  In  fact  under  these  conditions  there 
is  a  diminution  of  the  quantity  secreted  although  there  is 
an  increase  in  the  solids  contained  in  that  saliva  which 
is  secreted.  We  must  conclude,  therefore,  that  a  large 
part  of  the  increased  secretion  of  saliva  caused  by  im- 
pulses descending  the  chorda  tympani  depends  upon  the 
improved  blood  supply,  but  also  that  some  direct  effect 

i8 


DIGESTION 

upon  the  cells  of  the  gland  is  produced  by  impulses  de- 
scending its  cranial  nerve  supply. 

The  Sympathetic  Nerve  Supply  —  What  effect  is  pro- 
duced by  stimulating  the  sympathetic  ?  In  the  dog  only  a 
few  drops  of  viscid  saliva  follow  stimulation  of  the  sym- 
pathetic nerves  passing  to  the  submaxillary  gland  and  no 
secretion  at  all  from  the  parotid  gland.  In  the  cat  there 
may  be  a  copious  secretion  of  saliva  after  stimulation  of 
the  sympathetic  to  the  submaxillary  gland.  We  miist  re- 
member that  the  sympathetic  nerves  carry  constrictor  im- 
pulse to  the  blood  vessels.  The  degree  with  which  these 
constricting  impulses  are  effective  is  doubtless  a  factor  in 
the  different  secretory  effects  produced  in  various  animals 
by  stimulation  of  the  sympathetic  nerves. 

Although  stimulation  of  the  sympathetic  nerve  causes, 
in  general,  constriction  of  the  vessels  and  no  secretion  of 
saliva,  it  does  cause  a  marked  accumulation  of  granules 
in  the  cells  of  the  gland. 

Atropine  in  no  way  checks  the  formation  of  these  gran- 
ules. This  accumulation  of  granules  may  be  viewed  as 
the  first  step  in  the  formation  of  saliva.  They  are  present 
in  both  the  mucous  and  serous  glands,  though  of  larger 
size  in  the  former. 

In  the  resting  gland,  or  in  one  beginning  to  secrete, 
the  granules  are  very  numerous.  After  a  gland  has  been 
forced  to  secrete  for  six  to  seven  hours  the  granules  are 
much  fewer,  located  on  the  edge  of  the  cell  nearest  the 
lumen  of  the  gland  and  the  amount  of  protoplasm  in  the 
cell  is  relatively  or  absolutely  increased  in  amount,  al- 
though the  cell  itself  is  much  smaller. 

In  fact  the  act  of  secretion,  whatever  may  be  the  cause, 

20 


DIGESTION 

is  always  associated  with  the  formation  of  these  granules. 
Their  formation  is  a  conspicuous  result  of  stimulation  of 
the  chorda  tympani,  but  in  this  case  they  are  not  retained 
within  the  cell  or  rather  they  are  extruded  to  make  room 
for  newly  formed  granules. 

Summary  of  the  Nervous  Control  of  Secretion  of 
Saliva  —  In  conclusion,  regarding  the  effects  of  the 
double  nerve  supply  to  the  salivary  gland,  we  may  say 
that  — 

1.  Both  sets  of  nerves  produce  a  direct  effect  upon  the 
cells  of  the  gland. 

2.  That  this  effect  must  be  related  to  either  the  previ- 
ous existence  or  the  formation  of  granules  in  the  cells 
the  presence  of  which  we  may  regard  as  a  necessary  pre- 
lude to  secretion. 

3.  That  the  two  sets  of  nerves  differ  in  their  effects 
upon  the  blood  vessels  of  the  gland  and  that  this  improved 
blood  supply  to  the  salivary  glands  explains  in  part  the 
difference  between  the  effects  of  stimulating  the  cranial 
and  sympathetic  nerves  supplying  the  glands. 

4.  The  vascular  differences  certainly  in  a  large  part 
explain  the  different  action  of  impulses  descending 
through  these  two  sets  of  nerves.  We  may  consider  for 
instance  that  the  vaso  constriction  accompanying  stimula- 
tion of  the  sympathetic  reduces  these  nerves  to  the  same 
helplessness  as  a  stimulated  cranial  nerve  when  the  carotid 
is  clamped.  On  the  other  hand  the  fact  that  atropine 
effects  stimulation  of  the  cranial  nerves  differently  than 
the  sympathetic  nerves  is  evidence  that  the  endings  of  the 
cranial  nerve  supply  w^ithin  the  cell  is  somewhat  different 
and  affects  different  functions  of  the  cell  than  the  sym- 
pathetic nerve  supply. 

22 


DIGESTION 

The  Minute  Histological  Changes  Accompanying 
Secretion —  i.  As  a  direct  result  of  nuclear  activity,  a 
change  occurs  in  the  protoplasm  of  a  cell  during  secretion. 
It  becomes  more  basophilic  and  the  new  basophilic  sub- 
stance streams  out  in  the  form  of  filaments  away  from  the 
nucleus  in  the  surrounding  protoplasm.  These  filaments 
have  been  identified  as  the  active  agents  of  the  protoplasm 
in  the  manufacture  of  the  precursors  of  the  secretion. 
They  have  consequently  been  called  ergastoplasm. 

2.  Granules  are  now  formed.  They  first  appear  near 
the  inner  border  of  the  cell  and  later  near  its  free  border 
and  in  these  two  situations  give  different  staining  re- 
actions. Consequently  they  must  have  undergone  a  modi- 
fication in  their  passage  through  the  cell. 

3.  The  last  step  is  the  swelling  and  bursting  of  the 
granules,  and  the  discharge  of  their  contents  into  the 
lumen  of  the  alveolus.  Certain  reagents  demonstrate 
that  the  granules  within  the  cell  are  quite  different  from 
the  formed  secretion  of  the  gland. 

Acetic  acid  will  cause  the  granules  to  swell  up  and 
burst;  on  the, other  hand,  when  added  to  the  mucin  in  the 
fully  formed  secretion  it  precipitates  it  as  threads  or 
films. 

Mucin  does  not,  therefore,  exist  in  the  cell  but  a  fore- 
runner of  mucin  or  precursor  of  mucin,  which  has  been 
named  mucinogen.  In  the  same  manner  ptyalin  must 
exist  as  a  precursor  of  ptyalin  within  the  gland  cell. 

Demonstration  of  the  Dynamic  Character  of  the 
Act  of  Secretion  —  All  these  changes  occurring  within 
the  cell  mean  work  on  the  part  of  the  cell  as  contrasted 
with  a  simple  process  of  filtration  of  the  constituents  from 

24 


DIGESTION 

the  blood  through  the  cell.  The  fact  is  further  confirmed 
by  the  strong  pressures  under  which  the  gland  secretes. 
It  will  continue  to  secrete  against  a  pressure  in  its  duct 
which  is  double  that  in  the  carotid  artery. 

Moreover,  in  saliva  the  concentration  of  the  salts  is 
never  more  than  one-half  to  three-quarters  of  that  in  the 
blood.  It  is  possible  to  determine  the  concentration  of 
the  salts  in  the  two  fluids,  i.e.,  in  the  saliva  and  blood, 
by  a  comparison  of  their  freezing  points.  The  only 
manner  in  which  a  portion  of  the  salts  in  the  blood  could 
be  kept  back,  if  the  passage  of  the  salts  through  the  cell 
was  by  a  process  of  filtration,  would  be  by  the  pres- 
ence as  a  part  of  the  cell  of  a  semipermeable  mem- 
brane. We  would  be  obliged  to  assume  that  the  cell  con- 
stituted such  a  membrane. 

It  would  be  necessary  for  a  blood  pressure  ten  to 
twenty  times  as  large  as  the  normal  arterial  blood  pres- 
sure to  exist  in  the  capillaries  in  order  to  explain  the  dif- 
ference in  the  percentage  of  salts  in  the  saliva  and  blood 
upon  the  purely  physical  grounds  of  osmosis. 

If  we  inclose  a  salivary  gland  in  a  plethysmograph,  an 
instrument  for  measuring  its  changes  in  size,  we  will  find 
that  stimulation  of  the  chorda  tympani  will  cause  the 
gland  to  diminish  in  size  unless  the  secretions  of  the  gland 
have  been  checked  by  a  previous  administration  of  atro- 
pine. In  other  words,  notwithstanding  an  actual  increase 
in  the  amount  of  blood  which  the  gland  contains,  it  has 
actually  diminished  in  size  as  the  first  result  of  stimula- 
tion. 

Hence  the  first  act  in  secretion,  produced  by  the  im- 
pulses descending  the  cranial  nerve  supply  to  the  gland, 

26 


DIGESTION 

is  to  cause  the  cells  to  empty  themselves.  The  picking 
up  of  new  material  from  the  blood,  out  of  which  new 
granules  are  formed,  is  a  second  step.  These  activities 
cannot  be  passive  and  the  process  of  secretion  is  not  a 
passive  filtration. 

Electrical  Changes  Accompanying  the  Act  of  Secre- 
tion —  As  in  every  other  active  tissue  in  the  body  certain 
electrical  changes  accompany  secretion.  In  order  to 
measure  these  changes  the  terminals  of  a  circuit  through 
a  galvanometer  are  connected  to  the  hilum  of  the  gland 
and  its  outer  surface. 

There  will  be  a  deflection  of  the  needle  of  the  galvan- 
ometer indicating  a  resting  current,  in  such  a  direction 
that  the  hilum  is  negative  to  the  outer  surface  of  the 
gland. 

If  the  gland  is  stimulated  through  the  cranial  nerve 
supply  the  resting  currents  are  first  increased  (a  positive 
variation).     In  other  words,  a  diphasic  change  in  poten-' 
tial  has  passed  through  the  gland  with  the  act  of  secretion. 

Upon  stimulating  the  sympathetic  nerve  supply  there  is 
generally  a  negative  monophasic  variation. 

Inasmuch  as  no  secretion  follows  stimulation  of  the 
sympathetic  it  has  been  considered  that  the  negative  varia- 
tion accompanies  the  formation  of  granules  in  the  cells 
while  a  positive  variation  accompanies  the  passage  of 
fluid  through  the  cells  of  the  gland  and  into  the  duct;  in 
other  words,  there  is,  after  stimulation  of  the  chorda,  a 
passing  away  of  the  products  of  the  first  change. 

The  Energy  Involved  in  the  Act  of  Secretion  —  The 
energy  involved  in  the  act  of  secretion  is  considerable. 
By  the  resting  gland  .25  c.c.  of  oxygen  are  taken  from 


DIGESTION 

the  blood  and  .1700  of  carbon  dioxide  are  returned. 
During  secretion  .86  c.c.  of  oxygen  are  taken  up  and  .39 
c.c.  are  given  off.  Calculated  in  terms  of  heat  as  esti- 
mated by  an  equivalent  degree  of  oxidation  of  glucose,  a 
resting  gland  of  6  drams  weight  produces  i.i.  calories 
per  minute.  Much  external  work  is  done  during  secre- 
tion in  the  formation  of  a  fluid  of  less  concentration  than 
the  blood,  in  other  words  against  the  strong  force  of 
osmotic  pressure,  and  also  in  overcoming  the  resistance 
in  the  ducts,  a  resistance  which  may  even  be  much  higher 
than  the  blood  pressure. 

The  Essential  Nature  of  Secretion  —  Is  it  possible  to 
form  any  conception  of  the  nature  of  the  changes  in- 
volved in  secretion? 

There  are  in  the  first  place  cells  resting  upon  a  base- 
ment membrane  which  separates  them  from  tissue  spaces. 

The  tissue  spaces  are  lined  with  endothelium  and  con- 
tain lymph.  Through  the  tissue  spaces  wind  the  capil- 
laries containing  within  them  the  blood  current,  which  in 
turn  is  separated  from  the  tissue  spaces  by  the  en- 
dothelial cells  lining  the  capillaries.  Between  the  cells 
and  the  blood  there  exist  therefore  several  membranes. 

1.  The  basement  membrane  of  the  secreting  cells. 

2.  The  lining  of  the  lymph  spaces. 

3.  The  capillary  wall. 

There  is  a  free  interchange  between  the  lymph  spaces 
and  the  capillaries  by  simple  diffusion.  When  the  capil- 
laries are  well  filled  the  lymph  spaces  will  also  be  well 
niled  and  from  these  spaces  the  cells  of  the  gland  must 
obtain  the  chemical  substances  from  which  to  manufacture 
the  products  which  eventually  become  their  secretion. 

30 


DIGESTION 

The  first  change  after  stimulation,  at  least  of  the 
chorda,  seems  to  involve  the  granules.  They  become 
sw^ollen  and  hence  must  absorb  water  apparently  against 
osmotic  pressure.  They  must  obtain  the  water  from  the 
protoplasm  of  the  cell.  The  concentration  of  the  proto- 
plasm must,  therefore,  become  greater,  a  change  which 
would  induce  a  diffusion  of  water  from  the  lymph,  and 
the  latter  in  turn  a  diffusion  of  water  from  the  blood 
stream.  The  increased  concentration  of  the  j^rotoplasm 
of  the  cell  and  of  the  lymph  is  also  due  to  another  factor, 
namely  the  collection  of  metabolites  in  the  cell. 

We  know  that  chemical  changes  are  transpiring  within 
the  protoplasm  of  the  cell.  These  cannot  occur  without 
the  production  of  more  molecules  of  a  simpler  composi- 
tion within  the  protoplasm,  the  metabolites.  These  will, 
of  course,  increase  its  molecular  concentration.  As  a 
result  of  the  nuclear  activity,  the  protoplasm  itself  must 
be  regenerated  or  rebuilt. 

Insuperable  difficulties  surround  any  attempt  to  pene- 
trate further  into  the  processes  involved. 

We  might  consider  that,  as  a  result  of  the  stimulus, 
there  was  a  sudden  explosion  in  the  granules.  We  should 
then  have  a  sudden  multiplication  of  the  molecules  in  the 
granules.  This  would  cause  a  rise  of  osmotic  pressure 
in  them  with  the  absorption  of  water  from  the  surround- 
ing protoplasm. 

This  would  result  in  the  formation  of  a  fluid  having 
the  same  molecular  concentration  as  the  surrounding 
protoplasm,  unless  we  should  further  assume  that  before 
the  extrusion  of  the  granules  from  the  cell  or  its  mem- 
brane, there  was  a  further  breakdown  of  metabolites  with 

3^ 


DIGESTION 

the  production  of  carbon  dioxide  which  diffused  out  from 
the  cell.  As  a  corollary  to  this  explanation,  it  is  perfectly 
possible  to  assume  as  in  the  case  of  muscle  that  the  mem- 
brane of  the  granules  in  certain  stages  of  their  existence 
is  a  semipermeable  one  and  permits  the  passage  of  carbon 
dioxide  but  not  the  passage  of  other  substances. 

The  various  possibilities  concerning  physical  forces 
alone  unquestionably  play  a  part  in  the  dissimulatory 
activity  of  glandular  tissue. 

THE    PASSAGE    OF    FOOD    FROM    THE    MOUTH    TO    THE 
STOMACH. 

Methods  of  Study  —  A  number  of  methods  may  be 
utilized  to  study  the  physiology  of  deglutition. 

1.  A  bolus  of  food  may  be  mixed  with  bismuth  sub- 
nitrate  and  its  passage  from  the  mouth  to  the  stomach 
followed  by  successively  taken  radiographs  or  by  the  eye 
with  the  aid  of  the  florescent  screen. 

2.  Sounds  provided  with  rubber  balloons  attached  at 
dift'erent  levels  may  be  passed.  The  balloons  may  be  con- 
nected to  recording  tambours. 

3.  The  passage  of  food  or  liquid  through  the  esophagus 
is  accompanied  by  sounds.  The  first  sound  is  synchron- 
ous with  the  beginning  of  the  swallowing  act  and  is 
caused  by  the  impact  of  the  food  or  fluid  against  the  pos- 
terior pharyngeal  wall  and  doubtless  is  also  contributed 
to  by  the  squirting  of  the  food  through  the  narrow  en- 
trance to  the  esophagus.  It  is  heard  best  over  the  cervicai 
portion  of  the  esophagus. 

The  second  sound  is  heard  best  over  the  epigastrium 
and  is  synchronous  with  the  entrance  of  the  food  into 

34 


DIGESTION 

the  stomach  through  the  cardiac  orifice.  It  generally 
lasts  two  or  three  seconds  and  begins  four  to  ten  seconds 
after  the  first  sound.  If  the  individual  is  horizontal  or 
any  reason  exists,  such  as  a  stenosis  of  the  esophagus  at 
the  cardia,  why  the  passage  of  food  into  the  stomach 
should  be  delayed,  the  second  sound  is  converted  into  a 
series  of  squirts  anywhere  from  two  to  five  in  number. 

Both  the  Roentgen  and  auscultatory  methods  confirm 
each  other  regarding  the  time  occupied  in  the  passage  of 
food  to  the  stomach. 

Duration  of  Deglutition  —  The  time  varies  with  the 
position  of  the  individual  and  the  degree  of  dryness  of 
the  bolus  of  food.  If  dry,  as  much  as  fifteen  minutes 
may  be  consumed  from  the  time  the  bolus  has  passed 
from  the  mouth  before  it  enters  the  stomach.  If  dry  but 
well  moistened  on  its  outside,  eight  to  eighteen  seconds 
are  occupied  in  its  passage.  Fluid  will  pass  more 
rapidly,  six  seconds  is  the  average  length  of  time  re- 
quired before  the  last  traces  of  fluid  enter  the  stomach. 

Stages  of  Deglutition  —  Three  stages  are  generally 
recognized  in  the  act  of  swallowing. 

First  Stage  —  The  first  includes  the  passage  of  the 
food  over  the  back  of  the  tongue,  through  the  canal 
formed  by  the  pillars  of  the  pharynx.  The  second  stage 
is  occupied  by  the  passage  of  the  food  over  the  laryngeal 
opening  and  into  the  entrance  of  the  esophagus.  The  act 
is  started  as  a  voluntary  act  and  completed  as  an  involun- 
tary reflex.  The  first  step  is  the  elevation  and  retraction 
of  the  tongue  against  the  roof  of  the  mouth  and  the  pres- 
sure of  the  food  backwards  between  the  tongue  and  roof 
of  the  niDuth.      This  act  is  performed  bv  the  mylohvoid, 

36 


DIGESTION 

styloglossus  and  palatoglossus  muscles.  The  stylo- 
glossus and  palatoglossus  also  serve  to  prevent  the  return 
of  the  food  into  the  mouth  after  it  has  passed  the  pillars 
of  the  fauces.  The  food  must  next  traverse  a  region 
common  to  the  respiratory  and  alimentary  tracts.  It  is 
necessary,  therefore,  that  the  larynx  should  be  closed  and 
the  food  pass  over  it  as  rapidly  as  possible. 

Second  Stage  —  By  the  contraction  of  the  levator 
palati,  palato  pharyngeus  and  azygos  uvulae  muscles  the 
nasal  cavity  is  shut  off.  By  the  rotation  inwards  of  the 
arytenoid  cartilages  and  the  approximation  of  the  true 
and  false  vocal  cords  the  glottis  is  closed.  The .  ary- 
tenoids move  forward  and  the  epiglottis  moves  backward 
until  the  two  meet,  forming  a  triradiate  fissurCj  where 
the  free  edges  of  these  structures  are  in  contact.  The 
vertical  limb  lies  between  the  two  arytenoid  cartilates  and 
the  two  anterior  limbs  are  formed  by  the  drawing  inwards 
of  the  margins  of  the  epiglottis.  (The  following  muscles 
participate  in  producing  the  closure  of  the  laryngeal 
orifice  :  —  The  external  thyroarytenoid,  interarytenoid, 
the  aryteno-epiglottidean  and  the  cricoarytenoid.)  In 
this  closure  of  the  laryngeal  opening  there  is  a  definite 
movement  upward  of  the  whole  larynx.  The  movement 
upwards  is  made  possible  by  the  fixation  of  the  hyoid 
bone  and  by  the  contraction  of  the  muscles  attached  to 
the  upper  border  of  this  bone,  the  stylohyoid,  the  genio- 
hyoid and  geniohyoglossus,  but  especially  by  the  fixation 
of  the  base  of  the  tongue  by  the  contraction  of  the  mylo- 
hyoid. 

The  passage  of  the  food  over  the  respiratory  passage 
is    the    most    rapid    portion    of    the    act    of    deglutition. 

38 


DIGESTION 

Under  usual  conditions  it  does  not  occupy  more  than  .8  of 
a  second.  Its  propulsion  through  this  region  is  in  part 
due  to  the  initial  velocity  imparted  to  it  by  the  muscles  of 
the  tongue.  It  is  carried  onward,  however,  into  the  eso- 
phagus by  the  contractions  of  the  middle  and  superior 
constrictors. 

Third  Stage  —  The  food  then  enters  upon  the  third 
stage  in  its  passage  from  the  mouth  to  the  stomach, 
namely  its  descent  through  the  esophagus.  This  is  ac- 
complished partly  by  gravity,  depending  upon  the  char- 
acter of  the  food  swallowed,  and  by  the  contractions  of 
the  muscular  walls  of  the  esophagus. 

Muscular  Walls  of  the  Esophagus  —  The  muscle  of 
the  esophagus  is  composed  of  striated  muscle  in  its  cerv- 
ical region,  in  the  upper  thoracic  region  of  mixed  striated 
and  unstriated,  while  in  the  lower  third  of  smooth  muscle 
alone. 

The  Reflexes  Concerned  in  Deglutition  —  The 
movements  of  deglutition  in  the  mouth  at  the  beginning 
of  the  act  of  swallowing  are  responsible  for  the  initiation 
of  several  reflexes  which  constitute  an  essential  part  of 
deglutition. 

Inhibition  of  Respiration  —  The  first  reflex  is  an  inhibi- 
tion of  respiration.  If  respiration,  at  least  inspiration, 
is  continued  during  that  period  of  deglutition  when  the 
food  is  passing  over  the  larynx,  the  food  may  be  inspired 
into  the  trachea.  The  inhibition  of  inspiration  during 
the  beginning  of  deglutition  guards  against  this  accident. 
Through  the  glossopharyngeal  nerve,  afferent  impulses, 
excited  by  the  pressure  of  the  food  on  its  peripheral  end- 
ings in  the  mucous  memljrane  of  the  pharynx  and  back 

40 


DIGESTION 

of  the  tongue,  pass  up  to  the  medullary  center  which  con- 
trol deglutition.  Here  the}^  become  transformed  into 
efferent  impulses  which  in  turn  descend  through  the 
phrenic  and  intercostal  nerves,  causing  an  arrest  of  res- 
piration lasting  one  or  two  to  five  or  six  seconds,  accord- 
ing to  the  rapidity  of  the  swallowing  act,  until  the  food 
has  passed  over  the  larynx. 

Continued  Propulsion  tJiroiigh  the  Esophagus  —  The 
continued  propulsion  of  food  from  the  moment  it  is 
grasped  by  the  pillars  of  the  fauces  to  its  entrance  into  the 
stomach  is  the  result  of  a  reflex  act  through  other  efferent 
nerves.  Moreover  the  glossopharyngeal  is  not  the  only 
nerve  which  transmits  the  afferent  .impulses  which  excite 
deglutition.  It  is  doubtless  the  chief  nerve  but  the  mus- 
cular branches  of  the  fifth  nerve,  particularly  those  to  the 
mylohyoid  muscle,  also  transmit  afferent  impulses  which 
are  responsible  for  setting  into  operation  the  complicated 
coordinated  events  comprised  in  deglutition. 

Afferent  and  Efferent  Nerves  of  Deglutition  —  The 
afferent  impulses,  therefore,  travel  by  the  fifth  and  ninth 
cranial  nerves.  The  efferent  impulses  by  the  hypoglossal 
to  the  muscles  of  the  tongue  and  hyoid  bone  by  the  su- 
perior and  inferior  laryngeal  nerves  to  the  muscles  of  the 
larynx.  Through  these  nerves  the  larynx  is  closed ;  other 
efferent  impulses  pass  through  the  ninth  and  tenth  to  the 
muscles  of  the  pharynx  and  esophagus. 

Mechanism  of  Peristalsis  in  the  Esophagus  —  These 
last  impulses,  i.e.,  those  through  the  ninth  and  tenth 
nerves,  excite  those  muscles  which  carry  the  food  onward 
to  the  stomach,  after  it  has  passed  the  pillars  of  the 
fauces.     These   nerves   not   only   carry   impulses   which 

42 


DIGESTION 

stimulate  tlie  appropriate  muscles  to  contract  in  their 
proper  order  but  also  inhibitory  impulses  which  at  the 
proper  time  relax  the  normal  constrictions  at  the  entrance 
to  the  esophagus  and  at  the  cardiac  sphincter. 

The  first  act  in  deglutition  produces  inhibition  of  peri- 
stalsis in  the  esophagus.  It  is  only  after  this  is  com- 
pleted that  a  peristaltic  wave  is  excited  in  the  esophagus 
and  travels  from  one  end  to  the  other. 

If,  therefore,  peristalsis  in  the  esophagus  is  in  progress 
and  a  second  deglutitory  act  is  started,  the  peristaltic  w-ave 
in  the  esophagus  will  cease,  and  not  begin  again  until  the 
first  stage  of  the  second  act  of  deglutition  has  ceased. 

Deglutition  is,  therefore,  a  series  of  muscular  contrac- 
tions and  inhibitions  occurring  with  a  proper  sequence 
and  coordination  and  excited  by  afferent  impulses  passing 
to  the  brain  in  the  fifth  and  ninth  nerves  and  descending 
on  the  ninth  and  tenth  and  twelfth  nerves. 

DIGESTION    WITHIN    THE    STOMACH. 

Character  of  the  Gastric  Glands  —  Arrived  within 
the  stomach  the  food  collects  at  first  within  the  cardiac 
portion  of  the  stomach  and  becomes  subject  to  chemical 
changes  wrought  within  it  by  the  gastric  juice.  The 
whole  of  the  interior  of  the  stomach  is  lined  with  tubular 
glands ;  these  begin  to  pour  forth  their  secretion  within 
five  minutes  after  the  food  has  arri\ed  in  the  stomach. 

1\\()  kinds  of  glands  exist  in  the  stomach  — 

1.  Cardiac  glands. 

2.  IVloric  glands. 

Both  are  tul)ular  and  consist  of  a  long  neck-like  portion 
which  fulfills  the  function  of  a  duct  and  empties  into  a 

44 


DIGESTION 

pit  on  the  surface  of  the  mucous  membrane.  The  pit  also 
receives  the  ducts  of  several  other  tubules.  The  deepest 
portion  of  the  gland  is  called  its  fundus  and  is  to  be  re- 
garded as  the  secreting  portion.  Usually  the  duct  and 
fundus  are  separated  by  a  constricted  portion  lined  with 
a  cuboidal-shaped  cell.  The  duct  is  lined  with  columnar 
cells.  The  gland  itself  is  lined  in  the  cardiac  portion  of 
the  stomach  with  two  types  of  cells. — 

1.  Chief  cells. 

2.  Parietal  cells. 

The  chief  cells  in  general  are  columnar  though  some- 
what irregular.  They  are  responsible  for  the  secretion  of 
pepsin. 

The  parietal  cells  are  irregularly  cuboidal  in  shape  and 
lie  against  the  basement  membrane,  wedged  in  between 
the  chief  cells.  They  maintain  their  connection  with  the 
lumen  either  directly  or  by  clefts  between  the  chief  cells. 
They  stain  intensely  with  the  aniline  dyes  and  are  respon- 
sible for  the  secretion  of  the  acid  in  the  stomach. 

The  pyloric  glands  are  more  irregular  or  convoluted 
in  shape  and  consist  of  branched  tubules.  They  are 
lined,  with  exceptions  here  and  there,  with  only  chief  cells. 

Method  of  Collecting  Gastric  Juice  for  Study  —  Gas- 
tric juice  may  be  obtained  for  study  by  syphoning  off  the 
contents  of  the  stomach  at  varying  lengths  of  time  after 
the  administration  of  food.  It  may  also  be  obtained  from 
a  gastric  fistula  which  is  sometimes  present  in  the  normal 
human  being  or  can  be  created  for  experimental  purposes 
in  the  dog. 

General  Characters  of  Gastric  Juice  —  The  gastric 
juice  of  the  dog  contains  0.6  per  cent,  of  hydrochloric 

46 


DIGESTION 

acid ;  that  of  the  human  being  contains  0.2  per  cent,  of 
hydrochloric  acid.  As  a  result  of  fermentation  caused  by 
the  action  of  bacteria  upon  carbohydrates,  lactic  acid  may 
be  present;  the  acid  in  the  gastric  juice  stops  this  fer- 
mentation so  that  in  the  normal  stomach  during  the  later 
stages  of  digestion  all  lactic  acid  should  be  absent. 

Digestive  Changes  in  the  Food  Accomplished  by 
the  Acid  of  the  Gastric  Digestion  —  The  following 
changes  are  produced  solely  by  the  acid  in  the  gastric 
juice  — 

1.  Cane  sugar  is  split  apart  into  glucose  and  fructose. 

2.  Some  proteins  are  swollen  into  a  gelatinous  mass ; 
these  proteins  are  more  particularly  fibrin  and  the  col- 
lagen of  connective  tissue. 

3.  Many  proteins,  including  protamines,  histones,  albu- 
mins, whether  egg  albumin  or  serum  albumin,  and  the 
varieties  of  globulins,  are  transformed  by  weak  acids  into 
acid  albumin  or  acid  proteins. 

4.  They  are  soluble  in  weak  acids  or  alkalis  but  may  be 
precipitated  by  neutralization,  they  are  also  precipitated 
by  boiling  from  an  acid  solution.  By  the  acid,  therefore, 
many  proteins  may  be  transformed  into  soluble  proteins. 

Changes  Due  to  Pepsin  and  the  Products  of  Gastric 
Digestion  of  Proteins —  Gastric  juice,  in  addition  to  the 
acid,  contains  also  a  ferment  called  pepsin.  This  ferment 
in  an  acid  medium  is  capable  of  producing  a  series  of 
hydrolysed  jjroducts  from  proteins.  Each  product  rep- 
resents a  cleavage  product  of  a  smaller  sized  molecule 
than  the  preceding  body  from  which  it  itself  has  been 
derived.  Tliis  is  demonstrated  by  the  different  propor- 
tions of  the  amino  acid  contained  in  each.     The  products 

48 


DIGESTION 

in  the  order  in  which  they  are  formed  are  named  proto 
albumose,  hetero  albumose,  deutero  albumose  inckiding 
deutero  albumose  fraction  a,  b  and  c,  and  peptone  a  and 
peptone  b. 

The  albumoses  are  all  soluble  in  water,  in  weak  acids 
and  alkalis.  They  may  be  coagulated  and  they  are  all 
slightly  diffusible.  They  may  be  separated  from  each 
other  by  precipitation  with  varying  concentrations  of 
ammonium  sulphate  and  zinc  sulphate.  They  are  all  in- 
soluble in  saturated  solutions  of  sodium  chloride,  sodium 
sulphate,  zinc  sulphate  or  ammonium  sulphate. 

The  deutero  albumoses  are  soluble  in  approximately  a 
half  saturated  solution  of  ammonium  sulphate  while  the 
primary  or  proto  and  hetero  albumoses  are  not. 

The  peptones  differ  from  the  albumoses  in  being  sol- 
uble in  saturated  solutions  of  ammonium  sulphate  and 
the  other  neutral  salts  mentioned;  they  are  also  freely 
diffusible  through  an  animal  membrane. 

Changes  wrought  by  Gastric  Juice  on  Albuminoids 
and  on  Nucleo-proteins,  Phosphoproteins  and  on 
Casinogen  —  The  most  important  constituent  of  connec- 
tive tissue  is  collagen.  This  is  converted  into  gelatin 
by  the  gastric  juice  and  the  gelatin  then  converted  into 
the  gelatoses  and  gelatin  peptone. 

Elastin  is  the  chief  constituent  of  elastic  fibers.  It  may 
be  regarded  as  indigestible  in  the  stomach,  though  it  is 
acted  upon  by  a  prolonged  exposure  to  the  gastric  juice. 

Mucin  is  acted  upon  by  gastric  juice.  It  is  converted 
into  a  peptone-like  body  and  a  reducing  body  allied  to 
glycosamin. 

The  nucleo  proteins  are  split  into  their  protein  half, 

50 


DIGESTION 

which  is  converted  into  peptones,  and  their  nuclein  half 
which  Ijecomes  insoUible. 

The  phosphcproteins,  which  represent  all  proteins  con- 
taining a  phosphoric  acid  radical  in  organic  combination, 
and  are  represented  by  such  proteins  as  the  vitellin  of  egg 
and  caseinogen  of  milk,  undergo  a  somewhat  similar 
change  on  gastric  digestion  to  that  undergone  bv  the 
nucleo  proteins. 

A\'hen  caseinogen  is  introduced  into  the  stomach  con- 
taining gastric  juice  it  is  precipitated  in  the  form  of  a 
solid  clot  called  casein  provided  lime  salts  are  present. 
Evidence  exists  that  this  precipitation  is  due  to  a  special 
ferment  called  rennin :  on  the  other  hand  rennin  and 
pepsin  may  be  the  same  body. 

The  caseinogen  is  probably  first  split  into  a  soluble  por- 
tion and  an  insoluble  portion.  Tiie  evidence  for  this  con- 
sists in  the  fact  that  not  all  the  casein  clot  is  redissolved 
by  the  acid  gastric  juice.  The  former  in  the  presence  of 
lime  salts  becomes  transformed  into  the  clot-like  bodv 
casein.  Casein  becomes  digested  by  the  continued  action 
of  the  gastric  juice  into  caseinoses  and  peptones. 

Action  of  Fat  —  A  slight  amount  of  digestion  on  fat 
occurs  in  the  stomach.  In  virtue  of  this  action  a  small 
amount  of  fatty  acid  is  formed  in  the  stomach.  The 
digestion  of  fat  is  due  partly  to  the  free  hydrochloric  acid 
it.self  and  partly  to  a  special  ferment,  lipase,  secreted  in 
the  stomach. 


52 


DIGESTION 

THE  PHYSIOLOGY  OF   THE  SECRETION   OF  THE  GASTRIC 

JUICE. 

The  Factors  Involved  in  the  Secretion  of  Gastric 
Juice  —  Two  factors  cause  the  secretion  of  gastric  juice  : 

1.  A  reflex  nervous  mechanism. 

2.  The  presence  of  food  within  the  stomach. 

The  Method  of  Study  of  the  Secretion  of  the  Gastric 
Juice  — 

A.  Creation  of  Gastric  Fistula  — 

The  influence  of  the  two  factors  mentioned,  namely  the 
reflex  nervous  mechanism  and  the  local  effect  of  food 
within  the  stomach,  may  be  tested  separately  upon  an 
animal  such  as  a  dog  by  the  creation  of  a  gastric  fistula 
and  collection  therefrom  of  the  juice  secreted. 

In  such  an  animal  it  is  merely  necessary  to  show  the  ani- 
mal food  or  to  allow  it  to  smell  food  and  still  more 
effectually  to  allow  it  to  taste  it,  in  order  to  excite  the 
secretion  of  gastric  juice. 

B.  Esophageal  Fistula  — 

By  also  establishing  an  esophageal  fistula  in  the  neck 
the  animal  can  be  allowed  to  eat  food  without  any  of 
the  food  entering  the  stomach.  This  procedure  is  also 
accompanied  by  a  secretion  of  gastric  juice.  In  each  of 
these  cases  a  reflex  nervous  mechanism  is  a  factor  in  the 
secretion  of  the  gastric  juice.  In  the  first  case  the  reflex 
nervous  mechanism  is  not  the  sole  factor  and  as  a  conse- 
quence more  gastric  juice  will  be  secreted  than  in  an  ani- 
mal with  an  esophageal  fistula. 

Channels  of  the  Afferent  and  Efferent  Impulses  — 
The  afferent  stimuli  of  this  reflex  is  transmitted  to  the 

54 


DIGESTION 

brain  by  the  fifth  and  ninth  nerve  and  also  by  the  nerves 
of  sight  and  smell,  in  fact  by  very  many  channels.  Only 
one  nerve  transmits  the  efferent  stimuli ;  it  is  the  vagus  or 
tenth  nerve.  After  its  division  the  three  varieties  of 
stimuli  above  mentioned  are  powerless  to  evoke  a  secre- 
tion of  gastric  juice. 

Actual  Demonstrations  of  the  Path  of  Efferent  Im- 
pulses—  The  absolute  demonstration  of  efferent  secre- 
tory stimuli  in  the  vagus  nerve  by  stimulation  of  the  pe- 
ripheral segment  of  the  divided  vagus  nerve  can  only  be 
accomplished  by  allowing  the  cardio  inhibitory  fibers  in 
the  vagus  nerve  to  degenerate  before  trying  the  experi- 
ment. The  cardio  inhibitory  fibers  in  the  vagus  nerve 
will  degenerate  in  four  days'  time,  while  the  secretory 
nerves  to  the  stomach  after  this  period  will  be  still  func- 
tional. If  then  the  vagus  is  divided  in  the  neck  and  a 
thread  tied  around  its  peripheral  portion,  four  days  later 
this  portion  may  be  cautiously  pulled  out  of  the  wound, 
the  peripheral  end  may  be  stimulated  by  induction  shocks 
in  a  manner  to  excite  the  secretion  of  the  gastric  juice. 
The  latent  period  between  the  time  of  stimulation  and  the 
flow  of  gastric  juice  is  a  very  long  one. 

Hormonic  Secretion —  Stimulation  of  the  gastric  se- 
cretion by  means  of  the  nervous  mechanism,  whether  the 
stimulation  is  an  artificial  or  natural  one,  will  not  account 
for  all  the  gastric  juice  secreted.  The  total  amount  of 
gastric  juice  secreted  by  chewing  and  swallowing  food  so 
that  it  enters  the  stomach  in  the  natural  manner  is  far 
greater  than  that  obtained  by  invoking  the  reflex  nervous 
mechanism  alone.  The  secretion  of  gastric  juice  may, 
under  certain  circumstances,  be  stimulated  by  introducing 

5^' 


DIGESTION 

food  through  a  gastric  fistula,  the  animal  neither  smell- 
ing, seeing  nor  swallowing  the  food.  Such  a  secretion  is 
due  to  purely  local  effects. 

The  amount  and  strength  of  gastric  juice  secreted  in 
response  to  the  stimulus  of  eating  a  meal  in  the  normal 
manner,  that  is,  in  response  to  both  nervous  and  local 
stimuli,  is  equal  to  the  sum  of  the  amounts  secreted  in 
response  to  both  nervous  and  local  stimuli  when  sepa- 
rately applied. 

What  is  now  the  character  of  the  stimulus  to  secretion 
resulting  from  the  introduction  of  food  into  the  stomach? 
A  small  portion  of  the  stomach  may  be  separated  off  as  a 
diverticulum  from  the  main  gastric  cavity.  Both  these 
portions  are  made  to  communicate  with  the  exterior  by  a 
separate  fistulous  opening. 

One  may  secure  in  such  a  diverticulum  into  which  no 
food  has  been  introduced  a  gastric  secretion  which  has 
been  produced  by  the  stimulation  resulting  from  the  in- 
troduction of  food  into  the  main  cavity  of  the  stomach, 
and  this  secretion  may  then  be  compared  in  its  amount  and 
strength  with  that  secreted  in  the  portion  of  the  stomach 
into  which  the  food  has  been  introduced. 

The  proportionate  amount  and  the  strength  of  the  se- 
cretion collected  in  these  two  portions  of  the  stomach  are 
equal.  Why  should  they  be  equal?  What  is  the  nature 
of  the  influence  which  has  added  to  the  reflex  secretion 
in  the  portion  of  the  stomach  cut  off  from  contact  with 
food? 

Mechanical  Stimulation  to  Secretion  —  Is  the  me- 
chanical effect  of  the  food  within  the  stomach  the  cause 
of  the  secretion?     No,  because  it  is  impossible  to  excite 

58 


DIGESTION 

the  secretion  of  gastric  juice  by  rubbing  the  mucous  mem- 
1)rane  of  the  stomach  or  by  the  introduction  of  any  inert 
material  such  as  sand,  etc.,  within  it. 

Influence  of  the  Nature  of  Food  Introduced  — 
Aloreover  all  kinds  of  food  will  not  excite  the  secretion. 
White  of  egg  or  starch  or  bread  introduced  through  a 
fistula,  so  that  the  tgg,  starch  or  bread  is  not  swallowed, 
will  cause  no  secretion.  If,  however,  the  bread  or  egg  is 
digested  a  short  time  and  then  introduced  into  the 
stomach  within  a  short  time  there  will  be  a  copious  secre- 
tion of  gastric  juice. 

]\Ieat  is  effective  in  stimulating  a  secretion  even  without 
predigestion  and  still  more  powerful  yet  is  broth  or  the 
decoction  of  meat. 

Pure  albumoses  or  pure  peptones  have  no  effect  in 
stimulating  the  secretion  of  gastric  juice.  The  produc- 
tion of  the  juice  must,  therefore,  depend  upon  some 
chemical  substances  in  meat  or  manufactured  during  the 
digestion  of  food,  because  the  food  alone  without  diges- 
tion is  incapable  of  exciting  the  gastric  mucous  mem- 
brane. 

Failure  of  any  Nervous  Mechanism  in  the  Produc- 
tion of  this  Secretion  —  A  division  of  all  the  nerves 
connecting  the  stomach  with  the  central  nervous  system 
in  no  way  prevents  these  chemical  substances  from  act- 
ing. Do  they  then  act  upon  the  local  nervous  mechanism 
of  the  stomach  or  because  after  absorption  they  stimulate 
the  cells  directly  to  secrete? 

Effect  of  Injecting  Various  Substances  into  the 
Blood  Stream  —  It  has  been  shown  that  water  is  not 
absorbed  from  the  stomach.     One  may,  therefore,  inject 

60 


DIGESTION 

a  certain  quantity  of  fluid  into  a  stomach  and,  if  the 
pylorus  and  esophageal  opening  into  the  stomach  have 
been  shut  off  by  a  ligature,  recover  after  any  interval  the 
same  quantity  of  fluid.  If  the  quantity  has  been  increased 
or  is  distinctly  acid  or  possesses  digestive  powers  we  may 
be  sure  that  gastric  juice  has  been  added  to  the  fluid 
originally  injected. 

Edkins,  after  ligaturing  the  pyloric  and  cardiac  orifices 
of  the  stomach  and  filling  its  cavity  with  a  certain  amount 
of  water,  has  tried  the  effect  of  injecting  into  the  jugular 
vein  various  substances  which  might  be  supposed  to  be 
factors  in  stimulating  the  gastric  cells  to  secrete  after 
their  absorption   into  the  blood   stream. 

He  has  injected,  for  instance,  acid,  peptone,  broth, 
dextrin.  All  of  these  substances  produced  no  stimula- 
tion of  the  secretory  powers  of  the  gastric  cells. 

A  decoction  of  pyloric  mucous  membrane  with  acid 
or  with  water  or  with  peptone  introduced  in  small  quan- 
tities every  ten  minutes  into  the  circulation  caused  the 
gastric  cells  to  secrete  so  that  the  fluid  within  the  stomach 
upon  its  withdrawal  was  distinctly  acid  and  possessed 
digestive  powers. 

Only  the  decocted  pyloric  mucous  membrane  was  effec- 
tive. The  extracted  cardiac  mucous  membrane  excited 
no  activity  in  the  gastric  cells  when  injected  into  the 
circulation. 

The  chemical  principle  which  is  obtained  in  this  man- 
ner and  which  is  responsible  for  the  secretion  of  the 
gastric  juice  is  called  gastric  secretin  or  gastric  hor- 
mone.    It  is  significant  that  it  is  produced  in  that  por- 


62 


DIGESTION 

tion  of  the  stomach  where  absorption  is  most  pro- 
nounced. 

Intestinal  Gastric  Secretin  —  By  the  same  method 
experimental  evidence  has  been  produced  which  indicates 
that  a  hormone  for  gastric  secretion  is  also  produced  in 
the  small  intestine  but  not  in  the  large  intestine. 

Influence  of  Oil,  Alkalis  and  Acids  upon  Secretion 
of  Gastric  Juice  —  The  character  of  the  contents  of  the 
stomach  materially  influences  the  secretion  of  gastric 
juice.  The  ingestion  of  much  oil  diminishes  consider- 
ably the  amount  of  gastric  juice  secreted.  The  amount 
of  gastric  juice  secreted  is  much  diminished  by  the  in- 
troduction of  alkalis  and  increased  by  acids.  Indeed 
sodium  bicarbonate  diminishes  the  activity  of  the  digest- 
ive glands  throughout  the  alimentary  tract. 

Variations  in  the  Quantity  and  Quality  of  Gastric 
Juice  —  The  constituents  and  amount  of  gastric  juice, 
stimulated  by  psychic  or  reflex  stimuli,  are  not  altered  by 
the  character  of  food  ingested.  There  may,  however,  be 
considerable  variation  in  the  composition  and  amount  of 
the  hormonic  secretion.  The  total  amount  of  juice  se- 
■creted  is  greatest  with  meat  but  its  digestive  power  is 
greatest  when  bread  is  ingested. 

We  must  remember,  however,  that  these  facts  do  not 
necessarily  indicate  that  the  gastric  mucous  membrane 
possesses  specific  sensibilities.  Many  factors  enter  as 
possible  explanations  of  variations  in  the  relation  of  the 
amount  of  secretion  to  the  food  ingested.  The  strength 
of  the  psychical  stimuli  varies  with  the  appetite  and  the 
attractiveness  of  the  food  presented. 

The   quantity   of  juice  secreted   must  vary  with   the 

64 


DIGESTION 

-cjiiantily  of  hormone  and  the  latter  of  course  upon  the 
prehminar}^  stages  of  digestion  and,  therefore,  upon  the 
strength  of  the  psychical  stimuli. 

The  character  and  reaction  of  the  salts  present  in  the 
food  and  the  quantity  of  food  as  well  as  the  amount  of 
fluid  available  from  which  the  juice  may  be  formed  are 
all  factors  which  also  influence  the  amount  of  juice 
secreted. 

THE  PASSAGE  OF  THE  FOOD  THROUGH   THE  STOMACH 
AND    INTO    THE    INTESTINE 

Methods  of  Studying  the  Movements  of  the 
Stomach  —  The  movements  of  the  stomach  are  best 
studied  by  the  radiographic  method,  devised  by  Cannon. 
The  animal,  or  for  that  matter  a  human  being,  is  fed  a 
meal  in  which  a  cjuantity  of  bismuth  is  mixed.  The 
bismuth  is  far  less  easily  penetrated  by  the  X-rays  than 
the  tissues  of  the  body  or  the  stomach  wall. 

The  movements  of  the  stomach  of  an  animal  or  in- 
di\'idual  fed  in  this  manner  may  be  observed  directly  by 
means  of  the  floroscopic  screen  or  studied  by  examining 
a  series  of  radiographs  which  are  taken  at  short  inter- 
vals and  rapidly  passed  in  front  of  the  eye  in  a  manner 
to  reproduce,  in  a  moving  picture  fashion,  the  movements 
of  the  stomach. 

Delay  of  the  Food  in  the  Cardiac  Portion  of  the 
Stomach  —  A\Mien  food  enters  the  stomach  it  occupies 
at  first  the  cardiac  portion  or  at  least  what  may  be  de- 
scribed as  the  fundus  or  vertical  portion  of  the  stomach. 
This  portion  is  separated  from  the  rest  of  the  stomach, 
the  pyloric  portion,  in  animals  by  the  so-called  transverse 

66 


DIGESTION 

band  and  in  the  human  being  by  an  indenture,  the  in- 
cisura  angularis,  varying  at  different  times  in  its  dis- 
tinctness. 

Beginning,  Character,  Cause  of  and  Effect  Produced 
by  Muscular  Contractions  in  the  Stomach  and  The 
Factors  Controlling  the  Relaxation  of  the  Pylorus  — 
/Vfter  the  food  has  remained  in  the  fundus  or  vertical 
portion  of  the  stomach  for  twenty  to  thirty  minutes,  faint 
waves  of  contraction  begin  in  the  region  of  the  trans- 
verse band  or  the  incisura  angularis  and  proceed  toward 
the  pylorus.  As  the  waves  near  the  pylorus  they  l:;e- 
come  dee])er  and  as  digestion  proceeds  they  become  more 
regular,  deeper  and  stronger.  Reaching  the  pylorus  they 
force  a  little  fluid  through  as  a  little  scjuirt;  but  as  soon 
as  the  acid  of  the  gastric  juice  enters  the  duodenum  the 
pylorus  contracts  tightly  preventing  the  passage  into  the 
duodenum  of  any  more  fluid,  which  returns  in  the 
stomach  as  an  axial  stream. 

Any  solid  portions  of  the  contents  of  the  stomach  also 
stimulate  contraction  of  the  pyloric  opening. 

The  effect  of  the  peristaltic  waves  upon  the  pylorus  is 
further  increased  by  a  more  or  less  stead}^  tonic  contrac- 
tion of  the  cardiac  portion  of  the  stomach  which  presses 
its  contents  into  the  pyloric  portion.  The  peristaltic 
waves  in  the  pyloric  portion  of  the  stomach  recur  every 
fifteen  or  twenty  seconds.  They  progress  slowly  toward 
the  pylorus  so  that  three  or  four  are  present  at  one  time. 
As  the  fluid  within  the  duodenum  becomes  neutralized 
and  more  alkaline,  and  the  solid  masses  of  food  become 
dissolved  in  the  stomach,  the  pylorus  yields  more  readily. 

As  digestion  proceeds  the  pylorus  relaxes  to  a  greater 

68" 


DIGESTION 

degree  and  more  frequently  and  more  and  more  fluid 
passes  into  the  duodenum  until  finally  it  will  allow 
solid  masses  of  some  size,  even  large  foreign  bodies  such 
as  coins  or  pits  or  stones,  to  pass  it.  Mere  fluid  such  as 
warm  water  or  broth  will  pass  quickly  into  the  duodenum; 
a  large  draught  of  water  drunk  at  once  may  pass  into 
the  duodenum  in  a  minute  or  two. 

The  degree  with  which  the  pylorus  prevents  the  intra 
gastric  contents  from  entering  the  duodenum  bears  a 
direct  relation  to  the  acidity  of  the  contents  of  the  duo- 
denum. 

The  Nature  and  Origin  of  the  Muscular  Contrac- 
tions of  the  Stomach  —  We  see,  therefore,  that  the  con- 
tractions of  the  stomach,  by  which  it  moves  the  food 
around  within  itself  and  by  which  it  empties  itself  after 
a  definite  length  of  time,  may  be  described  as  coordinated 
movements.  Now  why  are  they  coordinated?  It  is 
quite  evident  that  the  origin  of  the  movements  must  be 
within  the  muscular  walls  of  the  stomach  itself.  Even 
an  excised  stomach  will  execute  these  movements. 
It-  is  quite  possible  that  the  coordination  of  the  move- 
ment between  the  fundus  and  pyloric  portion  may 
be  effected  by  the  local  nervous  mechanism  within  the 
stomach  wall,  the  plexus  of  Auerbach  and  Meissner.  No 
evidence  exists  that  after  throwing  the  local  nervous 
system  out  of  action  the  movements  persist.  Neverthe- 
less the  waves  do  not  resemble  a  true  peristalsis  because 
they  are  not  preceded  by  a  wave  of  relaxation.  They 
unquestionably  begin  within  the  muscular  fiber  itself  and 
are  therefore  truly  myogenetic. 

The  Control  of  the  Stomach  Movements  from  with- 

70 


DIGESTION 

out  by  the  Nervous  System  —  The  stomach  movements 
are  nevertheless  played  upon  or  modified  by  nervous  im- 
pulses from  without.  The  mechanism  by  which  the 
pylorus  controls  the  passage  of  food  into  the  intestine  is 
very  directly  under  the  control  of  the  nervous  system. 
The  most  important  nerve  passing  to  the  stomach  is  the 
vagus  nerve.  In  fact  how  far  the  sympathetic  nervous 
system  affects  the  stomach  is  not  known.  If  both  vagi 
are  divided  not  only  is  the  secretion  of  the  gastric  juice 
deficient  but  the  stomach  has  largely  lost  the  power  of 
emptying  itself.  In  fact  dogs  may  often  die  because  of 
sapremic  poisoning  due  to  absorption  of  putrefying  in- 
completely digested  food  which  has  been  retained  within 
the  stomach. 

If  a  gastric  fistula  or  pyloroplasty  is  made  conjointly 
with  the  division  of  the  vagus  nerve  the  animals  may  be 
kept  alive  for  months.  It  has  been  shown  that  the  in- 
jection of  acid  into  the  duodenum  will  cause  the  pylorus 
to  immediately  contract.  So  long,  therefore,  as  the  con- 
tents of  the  duodenum  are  acid  the  pylorus  will  remain 
firmly  contracted.  On  the  other  hand  increasing  acidity 
of  fluid  on  the  stomach  side  of  the  pyloric  sphincter  does 
not  prevent  relaxation  of  the  pyloric  sphincter.  When 
the  contents  of  the  stomach  are  alkaline  or  neutral  they 
will  freely  pass  into  the  duodenum  chiefly  because  of 
the  absence  of  the  reflex  controlling  the  pylorus  on  the 
duodenal  side,  but  if,  while  they  are  passing  into  the  duo- 
denum, acid  is  injected  into  the  duodenum  the  pylorus 
will  immediately  close.  The  character  of  this  response 
at  the  pylorus,  its  rapidity  as  well  as  its  occurrence  after 
division  of  the  vagi  nerves,  means  that  it  is  accomplished 

72 


DIGESTION 

by  a  local  nervous  mechanism   in  contrast  to  a  reflex 
through  the  central  and  nervous  system. 

Nature  of  the  Impulses  Descending  the  Vagus 
Nerve  of  the  Stomach  —  What  then  are  the  influences 
which  descend  through  the  vagus?  In  a  normal  animal 
stimulation  of  the  peripheral  end  of  the  divided  vagus 
nerve  produces  strong  contractions  of  the  esophagus  in- 
cluding the  cardiac  sphincter  of  the  stomach.  After  the 
administration  of  atropine  a  stimulation  of  the  vagus 
may  dilate  the  cardiac  sphincter.  There  must  be,  there- 
fore, within  the  vagus  inhibitory  fibers  for  the  cardiac 
sphincter. 

On  the  stomach  walls  itself  on  both  the  cardiac  and 
pyloric  portions  the  vagus  exercises  inhibitory  and 
augmentor  effects.  The  inhibitory  effects  seem  to  be  the 
first  to  follow  stimulation  of  the  vagus  nerve.  The  in- 
hibition, at  least  in  the  cardiac  region,  lasts  as  long  as  the 
stimulation.  It  is  immediately  followed  by  augmentation 
of  the  stomach  movements.  As  we  approach  the  pylorus 
the  inhibitory  effect  becomes  less  marked.  In  the  pyloric 
region  it  may  be  ver}'  brief  or  entirely  absent.  The  pre- 
vailing effect  of  the  vagus  nerve  upon  the.  stomach  is, 
therefore,  augmentor,  increasing  the  tone  of  the  cardiac 
region  and  the  peristalsis  of  the  pyloric  portion. 

It  produces  also  a  double  effect  on  the  pylorus  itself  and 
the  conditions  under  which  either  a  relaxation  or  con- 
■  traction  is  thus  produced  are  not  understood. 

It  is  possible  that  here  the  sympathetic  may  play  a  part 
and  the  presence  or  absence  of  sympathetic  impulses  may 
determine  whether  vagal  impulses  will  produce  relaxation 
or  contraction. 

74 


DIGESTION 


INTESTINAL    DIGESTION. 


The  Digestive  Fluids  Within  the  Intestines  —  After 
the  food  has  passed  from  the  stomach  into  the  intestines  it 
is  exposed  to  the  action  of  three  other  digestive  fluids. 
The  most  important  of  these  fluids  is  the  pancreatic  juice. 

The  Pancreas  and  its  Ducts  —  The  pancreatic  juice 
is  secreted  by  a  large  elongated  gland,  the  pancreas,  pos- 
sessing an  enlarged  right  extremity  called  the  head  and 
long  slender  left  extremity  called  the  tail.  The  pancreas 
stretches  horizontally  across  the  abdomen.  Its  head  is 
encircled  by  the  duodenum  and  lies  upon  the  second  lum- 
bar vertebra.  Its  tail  stretches  across  to  the  anterior  sur- 
face of  the  left  kidney.  The  gland  is  a  compound  race- 
mose gland  composed  of  tubules  hned  with  epithelial 
cells  which  empty  their  secretion  into  two  ducts.  One 
duct  runs  the  whole  length  of  the  gland  and  constitutes 
its  main  duct.  The  second  duct  is  smaller  and  is  named 
the  duct  of  Wirsung.  It  drains  the  upper  portion  of  the 
head  of  the  pancreas  which  is  further  removed  from  the 
course  of  the  main  duct.  The  duct  of  Wirsung  opens 
into  the  main  duct  a  short  distance  before  the  latter 
opens  into  the  intestines. 

The  two  ducts  have,  therefore,  a  common  opening. 
Usually  the  common  bile  duct  opens  with  them  into  the 
intestine.  The  common  opening  of  these  ducts  is  situated 
at  the  summit  of  a  little  papilla,  the  papilla  of  Vater, 
projecting  into  the  cavity  of  the  second  portion  of  the 
duodenum. 

Method  of  Study  of  the  Pancreatic  Juice  and  its 
Secretion  —  The  pancreatic  secretion  may  be  collected 

76 


DIGESTION 

for  study  by  transplanting  the  papilla  of  Vater  to  the 
surface  of  the  skin.  The  injection  of  secretin  or  pilo- 
carpine into  the  circulation  will  cause  the  gland  to  secrete. 
The  secretion  stimulated  by  pilocarpine,  however,  differs 
somewhat  in  quality  from  the  natural  secretion  of  the 
gland. 

Physical  Characters  and  Constituents  of  Pancreatic 
Juice  —  Pancreatic  juice  is  a  clear  slightly  opalescent 
strongly  alkaline  fluid.  Its  alkaline  reaction  is  due  to 
sodium  carbonate  and  amounts  to  a  Vw  to  Vi  normal  solu- 
tion of  sodium  carbonate.  This  strength  is  such  that  the 
pancreatic  juice  is  about  as  alkaline  as  the  gastric  juice 
is  acid. 

There  are  three  groups  of  proteins  in  pancreatic  fluid, 
one  a  nucleo  protein  precipitated  by  acid ;  a  second  coagu- 
lated at  55°  C,  and  another  coagulable  at  75°  C.  The 
later  secretion  of  the  gland  is  richer  in  alkalis  and  poorer 
in  proteins. 

Products  of  Protein  Digestion  by  the  Pancreatic 
Juice  —  Proteins,  or  at  least  the  albumins,  globulins,  pro- 
tamines and  histones,  are  transformed  by  the  alkali  into 
alkali  proteins.  These  are  then  transformed  by  its  pro- 
tein splitting  ferment,  trypsin,  into  albumoses  and  pep- 
tones precisely  as  the  acid  albumin  of  the  stomach  is  trans- 
formed into  albumoses  and  peptones. 

By  the  pancreatic  juice  this  change,  which  it  must 
always  be  remembered  is  a  splitting  apart  of  the  protein 
molecule  into  smaller  and  smaller  components  or  chemical 
units,  as  we  have  called  them,  is  carried  much  further 
than  is  the  case  with  gastric  digestion.  Moreover,  in 
addition  to  the  pei)tone  of  gastric  digestion,  another  kind 


DIGESTION 

of  peptone  appears  to  be  formed.  This  other  variet}^  of 
peptone  is  distinguished  by  its  resistance  to  further  diges- 
tion. It  is,  therefore,  called  antipeptohe.  Even  after 
weeks  of  exposure  to  the  action  of  trypsin,  a  portion  is 
left  which  gives  the  biuret  reaction,  a  reaction  which  is 
characteristic  for  peptone.. 

A  large  portion  of  the  peptone,  however,  rapidly  breaks 
down  into  the  amino  acids  or  the  smaller  chemical  units 
of  protein.  Even  within  a  few  minutes  after  the  chyme 
has  entered  the  intestines  some  amino  acids  will  have  been 
formed.  Leucin  and  tyrosin  are  cjuickly  formed  and 
were  among  the  first  products  known. 

A  good  idea  of  the  changes  accomplished  by  pancreatic 
digestion  upon  proteins  may  be  ascertained  by  examining 
the  products  of  digestion  after  one  hour,  after  a  day  and 
after  a  month.  After  one  hour  there  will  be  present  a 
soluble  coagulable  protein,  deutero  albumose,  peptone, 
amino  acids  and  a  small  amount  of  alkali  albumen. 

After  a  day's  digestion  there  will  be  present  deutero 
albumose,  antipeptone,  amino  acids  and  polypeptids. 

After  one  month's  digestion  there  will  only  be  present 
amino  acids  and  polypeptids.  The  trypsin  which  is  de- 
veloped from  the  tr3qDsinogen  of  the  pancreatic  juice,  as 
will  be  explained,  is  the  active  agent  in  this  breaking  apart 
of  the  protein  molecule.  The  breaking  apart  seems  to 
occur  where  the  polypeptids  and  amino  acids  are  united 
by  the  CO  and  NH  groups. 

Conditions  Affecting  the  Action  of  Trypsin  —  Only 
small  differences  in  the  structure  of  the  polypeptids  are 
sufficient  to  prevent  their  cleavage  by  trypsin.  Trypsin 
seems  only  to  act  upon  the  special  grouping  which  occurs 

80 


DIGESTION 

in  the  protein  molecule.  While  for  instance  it  will  split 
alanine  glycine,  it  will  not  affect  glycine  alanine. 

Trypsin  acts  most  strongly  in  an  alkaline  medium  and 
the  more  trypsin  which  is  present  the  stronger  is  the  de- 
gree of  alkalinity  which  is  most  favorable  to  its  action. 
Inasmuch  as  the  reaction  of  the  chyme  is  acid  this  fluid 
neutralizes  the  alkalinity  of  the  pancreatic  juice  when  the 
two  meet  in  the  intestine.  The  reaction,  therefore,  of 
the  intestinal  contents  is  neutral  and  this  neutrality  of  re- 
action obtains  as  a  rule  throughout  the  whole  of  the  small 
intestine.  Though  trypsin  acts  most  strongly  in  an  al- 
kaline medium  it  is  destroyed  by  an  alkaline  solution. 
The  neutral  reaction  in  the  intestines  tends,  therefore,  to 
render  its  action  more  prolonged.  With  proteins,  and 
their  components,  the  peptones  and  amino  acids,  trypsin 
forms  combinations  and  these  combinations  protect  the 
trypsin  from  further  destruction.  These  combinations 
remove  trypsin  from  the  sphere  of  action  so  that,  as 
they  are  formed,  and  particularly  in  an  excess  of  pro- 
teins, the  digestive  action  performed  by  trypsin  diminishes 
in  velocity. 

In  some  manner  the  trypsin  is  liberated  as  the  amino 
acids  are  removed  by  absorption.  Nevertheless  the 
sum  total  of  these  changes  results  in  the  fluid  within  the 
lower  end  of  the  ileum  possessing  little  or  no  proteolytic 
activity. 

The  Transformation  of  Trypsinogen  into  Trypsin 
and  the  Nature  of  Enterokinase  —  It  has  been  said 
that  trypsin  is  formed  from  trypsinogen ;  and  that  until 
this  change  has  been  effected,  pancreatic  juice  is  incapable 
of  affecting  proteins.     The  change  of  trypsinogen  into 

82 


DIGESTION 

trypsin  is  not  accomplished  in  the  act  of  secretion.  Pan- 
creatic juice  collected  directly  from  the  duct  of  the  gland 
without  contact  with  the  intestinal  mucosa  is  absolutely 
devoid  of  proteolytic  action. 

If,  however,  the  pancreatic  juice  is  mixed  with  a  little 
secretion  of  the  intestinal  mucous  membrane,  the 
trypsinogen  which  it  contains  becomes  cjuickly  trans- 
formed into  trypsin  and  the  juice  capable  of  proteolytic 
activity. 

-  The  intestinal  secretion  is  called  succus  entericus,  and 
the  active  principle  which  it  contains  and  which  trans- 
forms the  trypsinogen  is  called  enterokinase. 

The  enterokinase  must  be  regarded  as  a  ferment. 
Minute  cjuantities  are  capable  of  producing  relatively  large 
amounts  of  trypsin,  amounts  which  are  not  proportional 
to  the-  amount  of  enterokinase  used  to  produce  the 
trypsin. 

Increasing  or  diminishing  the  amount  of  enterokinase 
does  not  alter  the  quantity  of  trypsin  formed  from  the 
trypsinogen  acted  upon. 

Trypsinogen  may  be  converted  into  trypsin  by  other 
means  as  follows :  — 

1.  Simply  by  allowing  it  to  stand  with  toluol  to  pre- 
vent bacterial  decomposition. 

2.  Neutralization  will  hasten  this  change. 

3.  The  presence  of  lime  salts  will  convert  trypsinogen. 
None  of  these  means  are  as  powerful  as  enterokinase. 

The  most  powerful  of  all  these  other  means  is  the  pres- 
ence of  lime  salts  and  yet  even  these  salts  will  require 
many  liours  to  accomplish  what  enterokinase  can  accom- 
plish in  a  few  minutes'  time.     IMoreover  sodium  floride 

84 


DIGESTION 

which  win  prevent  the  spontaneous  transformation  of 
trypsinogen  into  trypsin  will  in  no  way  prevent  the  action 
of  enterokinase  on  trypsin. 

Action  of  Pancreatic  Juice  on  Milk  —  Milk  is  rapidly 
clotted  by  pancreatic  juice;  but  the  clot  very  rapidly  dis- 
solves. It  is  not  known  whether  this  change  is  to  be  as- 
cribed to  trypsin  or  another  rennet-like  ferment. 

Amylopsin  and  the  Action  of  Pancreatic  Juice  on 
Carbohydrates  —  Pancreatic  juice  contains  a  ferment 
W'hich  is  capable  of  transforming  starch  into  sugar.  The 
ferment  is  called  diastase  or  amylopsin. 

This  ferment  produces  precisely  the  same  series  of 
products  from  starch  which  ptyalin  produces;  but  as 
trypsin  carries  the  proteolytic  changes  further  than  pepsin, 
so  pancreatic  juice  carries  the  hydrolysis  of  starch  fur- 
ther. The  final  product,  maltose,  is  split  into  dextrose. 
This  last  change,  however,  is  not  accomplished  by  the 
amylopsin  but  by  a  second  ferment  called  maltase. 

The  other  disaccharides,  lactose  and  saccharose,  are 
not  hydrolysed  by  pancreatic  juice. 

Action  of  Pancreatic  Juice  on  Fats  and  Lipase  — 
A  fourth  ferment  which  pancreatic  juice  contains  is  li- 
pase. Lipase  is  a  strong  fat-splitting  ferment.  It 
hydrolyses  the  three  neutral  fats,  the  triglycerides  of 
palmitic,  stearic  and  oleic  acids  into  glycerine  and  the 
fatty  acid  components. 

Lipase  will  act  in  either  an  alkaline  neutral  or  slightly 
acid  medium.  If  the  fatty  acid  is  split  off  in  an  alkaline 
medium  the  alkali  base,  sodium,  if  the  alkaline  reaction 
is  due  to  sodium  carbonate,  replaces  the  glycerine  radical 
of  the  fat,  producing  a  sodium  salt  of  the  fatty  acid  in 

86 


DIGESTION 

which,  however,  the -sodium  replaces  the  h3'drogen  atom 
of  the  hydrox}'!  group  of  the  fatty  acid.  This  combina- 
tion is  called  a  soap.  Thus,  by  the  digestion  of  fats 
glycerine,  fatty  acids  or  soap  may  be  produced. 

Lipase  is  destroyed  by  trypsin  and  is  insoluble  in  water 
but  easily  soluble  in  one  of  the  products  of  its  own  diges- 
tion of  fats,  namely,  glycerine. 

The  Influence  of  Bile  on  the  Action  of  Lipase  — 
Bile  increases  four  or  five  times  the  velocity  of  the  action 
of  lipase  on  fat.     It  does  this  because  it  — 

1.  Diminishes  the  surface  tension  between  water  and 
fat.  This  results  in  the  formation  of  smaller  droplets  of 
fat  which  become,  therefore,  more  accessible  to  lipase. 

2.  Bile  is  a  good  solvent  of  lipase. 

3.  Bile  is  a  good  solvent  of  fatty  acids  and  soaps. 
Lipase  will  also  split  many,  if  not  nearly  all,  esters  of 

fatty  acids.  In  how  far  it  will  act  upon  the  phosphorized 
fats  or  the  phosphatides  is  still  a  matter  of  doubt. 

The  Factors  Concerned  in  the  Secretion  of  Pancre- 
atic Juice  —  These  may  be  studied  by  properly  creating 
a  pancreatic  fistula. 

a.  Nervous  Excitation  —  In  the  fasting  animal  there  is 
no  secretion  of  pancreatic  juice.  Within  one  to  one  and 
a  half  minutes  after  a  meal  the  secretion  of  pancreatic 
juice  begins. 

1).  Presence  of  Acid  in  the  Intestine- — The  secretion 
gradually  increases  for  tw(j  or  three  hours  and  then 
gradually  diminishes;  the  largest  amount  of  juice  escapes 
when  the  food  first  begins  to  ]:)ass  from  the  stomach  into 
the  duodenum. 

Paralleling  this  fact  the  injection  of  hydrochloric  acid 

88 


DIGESTION 

into  the  duodenum  increases  the  flow  of  pancreatic  juice. 
It  makes  a  difference,  however,  into  which  portion  of 
the  intestine  the  acid  is  injected.  The  amount  of  the  re- 
sponse to  the  injection  of  acid  diminishes  progressively  as 
the  ileum  is  approached. 

c.  Presence  of  Oil  in  the  Intestines  —  A  small  stimula- 
tion of  pancreatic  juice  follows  the  passage  of  oil  from 
the  stomach  into  the  duodenum. 

d.  The  Control  of  Secretion  through  the  Vagus  Nerve 
—  Is  the  stimulation  of  pancreatic  secretion  by  these 
various  means  the  result  in  part  or  in  whole  of  reflex 
action?  Certainly  in  part.  If  the  vagus  nerve  is  di- 
vided in  the  neck  and  time  allowed  for  the  degeneration 
of  its  cardiac  inhibitory  fibers,  weak  stimulation  of  its 
peripheral  end  will  result  in  a  flow  of  pancreatic  juice. 

If  the  vagus  is  divided  below  the  heart  immediate 
stimulation  of  its  peripheral  end  will  cause  a  flow  of  pan- 
creatic juice.  Under  certain  conditions  stimulation  of  the 
sympathetic  nerves  will  cause  a  secretion  of  pancreatic 
juice. 

It  is  quite  clear,  therefore,  that  these  nerves,  or  at  any 
rate  the  vagus,  carry  efferent  secretory  fibers  to  the  pan- 
creas and  we  may  conclude  that  this  gland  may  be  ex- 
cited to  secretion  through  a  central  reflex  action. 

e.  Tlie  Chemical  or  Honnonic  Stimnlation  of  the  Se- 
cretion of  Pancrc.tic  Juice  —  The  normal  stimulation  of 
the  pancreatic  juice  is  not  alone  by  reflex  action.  After 
division  of  both  vagi  and  destruction  of  the  sympathetic 
ganglia,  the  injection  of  acid  into  the  intestines  will  evoke 
a  secretion  from  the  pancreas.  The  injection  of  acid  is 
equally  successful  when  it  is  made  into  a  loop  of  intestine 

90 


DIGESTION 

entirely  severed  from  any  nervous  connections  with  the 
rest  of  the  body. 

The  only  connection,  therefore,  remaining  between  the 
loop  injected  and  the  pancreas  is  a  vascular  one.  We 
must,  therefore,  believe  that  some  chemical  substance  has 
been  absorbed  from  the  intestine  and  been  carried  to  the 
pancreas  and  there  has  stimulated  it  to  secrete. 

The  injection  of  acid  into  the  circulation  is  without 
effect  on  the  pancreas.  There  must  be  developed,  there- 
fore, in  the  presence  of  acid,  within  and  through  the 
agency  of  epithelial  cells  of  the  intestine,  a  substance 
which,  carried  from  the  intestines  to  the  pancreas  in  the 
blood,  possesses  the  power  of  stimulating  the  pancreatic 
secretion. 

Actual  Demonstration  of  the  Existence  of  Secretin 
—  If  the  epithelial  cells  are  pounded  up  with  weak  acid 
and  the  filtered  contents  injected  into  the  circulation,  there 
will  be  a  copious  secretion  of  pancreatic  juice.  The 
active  substance  developed  in  this  manner  is  a  hormone. 
It  is  called  secretin. 

Secretin  exists  not  as  such  in  the  epithelial  cells.  It 
requires  the  extraction  with  acid  to  produce  it :  a  fore- 
runner, therefore,  of  secretin,  called  prosecretin,  exists 
in  the  epithelium. 

Preparation  and  Properties — Secretin  is  not  a  fer- 
ment. It  may  be  prepared  in  a  partly  purified  form  by 
boiling  the  groundup  epithelial  cells  with  0.4  per  cent, 
hydrochloric  acid,  carefully  neutralizing  and  filtering. 
The  proteins  will  then  be  precipitated  by  coagulation  and 
the  secretin  will  be  in  the  filtrate. 

It  is  not  precipitated  by  alkalis  and  diffuses  slowly.     It 

92 


DIGESTION 

is  very  stable  in  acid  media  but  fairly  rapidly  destroyed 
by  alkaline  or  neutral  fluids  especially  if  many  bacteria 
are  present.  Solutions  of  soap  also  extract  it  from  mu- 
cous membranes. 

These  characteristics  adapt  it  admirably  for  the  pur- 
pose of  provoking  the  secretion  of  pancreatic  juice  for 
correct  lengths  of  time  and  at  the  time  physiologically 
most  favorable  after  the  ingestion  of  a  meal. 

Histological  and  Gross  Changes  Accompanying  the 
Act  of  Secretion  by  the  Pancreas  —  As  in  the  case  of 
the  salivary  glands,  there  are  marked  histological  changes 
accompanying  the  secretion  of  the  pancreatic  juice.  A 
normal  resting  pancreas  is  opaque  and  yellowish  Avhite 
in  color.  Examined  microscopically  the  intercalary  tub- 
ules are  narrow  and  the  cells  of  the  tubules  are  crowded 
with  granules.  These  granules  occupy  the  internal  two- 
thirds  or  three-fourths  of  the  cell.  They  are  strongly 
acidophilic. 

The  outer  one-fourth  or  one-third  of  the  cell  is  baso- 
philic. After  a  prolonged  period  of  activity  the  gland 
shows  definite  changes.  Its  color  has  changed  to  a  pink 
and  appears  transparent  and  much  softer  in  consistence ; 
on  microscopical  section  the  cells  are  smaller  and  contain 
fewer  granules.  These  are  collected  in  a  narrow  zone 
near  the  duct.  The  outer  basophilic  zone  has  greatly  in- 
creased. 

Islands  of  Langerhans  —  Throughout  the  pancreas 
appear  islands  of  cells  which  stain  with  greater  difficulty 
than  the  rest  of  the  pancreatic  cells.  These  islands  are 
called  the  islands  of  Langerhans.  They  become  more 
numerous  and  larger  in  a  gland  \\hich  has  been  forced 

94 


DIGESTION 

to  secrete  a  longer  time.  In  an  exhausted  pancreas  large 
portions  of  the  gland  have  lost  both  their  acidophilic  and 
basophilic  staining  cjualities  so  that  the  cells  composing 
these  tracts  cannot  be  differentiated  from  those  of  the 
islands  of  Langerhans. 

.Attempts  have  been  made  to  identify  these  islands  with 
carbohydrate  metabolism  but  it  is  questionable  whether 
they  should  be  viewed  as  performing  a  different  function 
than  the  rest  of  the  pancreas.  Their  failure  to  undergo 
atrophy  in  contrast  to  the  rest  of  the  pancreas  following 
a  ligature  of  the  duct  and  the  coincident  failure  of  diabetes 
to  appear  in  such  animals  strongly  supports  the  view  that 
the  islands  of  Langerhans  perform  a  different  function 
than  the  rest  of  the  pancreas. 

In  the  embryo,  a  large  portion  of  the  pancreas  gives 
the  staining  characteristics  of  the  islands  of  Langerhans. 

THE   DIGESTIVE    FUNCTION    OF   THE   BILE. 

The  Bile  Ducts  and  Gall  Bladder  —  The  bile  is  ex- 
creted by  the  liver  and  flows  into  the  intestine  through 
rather  a  long  duct,  the  common  bile  duct,  which  collects 
the  bile  from  the  separate  ducts  of  each  lobe  of  the  liver. 

This  duct  passes  to  the  intestine  through  the  layers  of 
the  lesser  omentum.  In  this  situation  it  occupies  an  in- 
timate relation  to  the  portal  ^•ein  and  hepatic  artery. 

Arri^•ed  at  the  intestine  it  passes  behind  the  second 
])(jrtion  of  the  duodenum  and  then  obliquely  through  its 
walls  to  open  into  the  ca\ity  of  the  latter  by  an  opening 
common  to  it  and  the  pancreatic  duct.  A  short  distance 
below  the  place  of  union  of  the  ducts  from  the  right  and 
left  lobe  of  the  liver  the  gall  bladder  opens  into  the  com- 

96 


DIGESTION 

mon  bile  duct  by  a  short  duct  of  its  own  called  the  cystic 
duct.  Provision  is  made  by  the  existence  of  the  gall 
bladder  for  the  storage  of  bile  during  the  time  in  which 
it  is  not  needed  for  digestive  purposes  in  the  intestine. 

Changes  Produced  in  the  Bile  during  its  Storage  in 
the  Gall  Bladder  and  Normal  Constituents  of  Bile  — 
During  the  period  in  which  the  bile  remains  in  the  gall 
bladder  it  becomes  concentrated  by  the  loss  of  water  and 
the  addition  to  it  of  mucin  and  nucleo  albumin  secreted 
from  the  cells  lining  the  gall  bladder.  The  chief  con- 
stituents of  the  bile  and  the  relative  amounts  present  in  the 
bile  coming  directly  from  the  liver  and  that  stored  in  the 
gall  bladder  are :  — 

BILE    FROM    A    FISTULA  BILE  FROM   A   GALL  BLADDER 

Mucin     and     bile     pigments  Mucin    and    bile    pigments 

bilirubin    and    biliverdin     .148  bilirubin   and   biliverdin  1.29 

Sodium   tauorcholate    0.055  Sodium  tauorcholate   0.87 

Sodium   glycocholate    0.165  Sodium  glycocliolate   3.03 

Cholesterin      "|  Cholesterin    35 

Lecitbin  l- 0.038  Soaps    1.39 

Fats  J  Lecithin    53 

Salts     0.840  Fats 73 

Water 98.7 

Functions  of  Bile  Pigments  and  Salts  —  The  bile 
pigments  must  be  viewed  entirely  as  excretory  products. 
After  entrance  into  the  intestine  they  are  converted 
mainly  by  bacterial  action  into  stercobilin,  which  forms 
the  pigment  of  the  feces.  A  small  portion  of  the  pig- 
ment is  absorbed  to  be  excreted  by  the  urine  as  urobilin. 

The  bile  salts  of  glycocholic  and  taurocholic  acid  and 
the  lecithin  and  cholesterin  are  the  important  digestive 
constituents  of  the  bile. 

98 


DIGESTION 

The  Secretion  of  Bile  —  The  factors  concerned  in  the 
stimulation  of  the  secretion  of  the  bile  may  be  studied 
by  creating  a  bihary  fistula.  In  forming  this  fistula,  as  in 
the  case  of  the  pancreatic  fistula,  it  is  wise  to  excise  the 
whole  papilla  of  Vater  and  a  portion  of  the  surrounding 
mucous  membrane,  stitching  the  same  to  the  skin. 

Method  of  Study  —  The  flow  of  bile  from  such  a 
fistula  will  run  parallel  with  the  secretion  of  pancreatic 
juice.  It  is  secreted  in  a  smaller  amount  than  the  pan- 
creatic juice  but  varies  with  the  latter  after  meals.  It 
begins  almost  immediately  after  taking  food  and  attains 
its  maximum  about  three  hours  after  eating  and  then 
rapidly  diminishes.  A  meal  of  meat  is  accompanied  with 
a  large  flow  of  bile  and  a  meal  of  carbohydrates  with 
a  comparatively  small  flow.  The  same  facts  are  true  of 
the  pancreatic  fluid. 

The  Two  Sources  Contributing  to  the  Flow  of  Bile 
into  the  Intestines —  In  the  flow  of  bile  from  the  open- 
ing of  the  orifice  of  the  duct  two  factors  are  involved: 

1.  The  amount  poured  forth  from  the  gall  bladder. 

2.  The  amount  coming  directly  from  the  liver. 

The  Relative  Part  Played  by  Each  - —  When  these  two 
factors  are  investigated  separately  by  comparing  the  flow 
from  a  fistula  of  the  common  duct  with  that  from  a 
fistula  of  the  gall  bladder  certain  differences  are  noticed. 
In  animals  with  a  fistula  of  the  gall  bladder,  the  common 
duct  being  ligatured,  it  will  be  found  that  the  secretion 
of  bile  is  continuous  but  that  the  secretion  of  bile  is  much 
increased  synchronously  with  the  normally  occurring 
periods  of  increased  flow  of  bile  from  the  fistula  of  the 
common  duct,  as  for  instance  three  hours  after  a  meal. 

I  GO 


DIGESTION 

The  emptying  of  the  gall  bladder  must,  therefore,  be  a 
gradual  process.  The  discharge  of  bile  from  the  liver 
cells  and  from  the  gall  bladder  must  be  subject  to  the 
same  stimuli. 

The  Nervous  Control  of  the  Gall  Bladder  —  The 
muscular  walls  of  the  gall  bladder  are  supplied  by 
Ijranches  of  the  vagus  and  sympathetic  nerves.  The 
vagus  conveys  motor  impulses  to  the  gall  bladder  and 
the  sympathetic  nerves  inhibitory  impulses. 

The  acid  chyme  enters  the  duodenum  and  excites  there 
afferent  impulses  which  cause  efferent  motor  impulses  in 
the  vagus  nerve  to  the  gall  bladder.  ^ 

The  exact  paths  of  this  reflex  are  not  known.  It  is 
natural  to  suppose  that  the  emptying  of  the  gall  bladder 
would  be  a  true  reflex.  It  may  be  provoked  by  the  in- 
jection of  acid  into  the  intestine. 

The  Cause  of  the  Increased  Production  of  Bile  by 
the  Liver  —  The  production  of  bile  by  the  liver  cells  is 
quite  another  matter  and  certainly  depends,  at  least  in  a 
large  part,  upon  the  production  and  absorption  of  se- 
cretin from  the  intestines. 

Injection  of  secretin  into  the  circulation  doubles  the 
flow  of  bile  from  the  common  duct  during  the  next  fif- 
teen minutes  after  the  injection. 

The  Digestion  Power  of  Bile  —  The  only  ferment 
which  bile  contains  is  a  weak  amylolytic  ferment. 
Nevertheless  in  the  presence  of  bile  the  proteolytic  power 
of  the  pancreatic  juice  is  doubled,  the  amylolytic  power 
is  doubled  and  the  lipolytic  power  is  trebled. 

This  augmentation  of  the  power  of  the  pancreatic  fer- 
ments by  bile  is  due  simply  to  its  solvent  emulsifying 

1 02 


DIGESTION 

properties.  For  this  reason  its  greatest  digestive  action 
is  upon  fats.  It  attacks  them  in  the  following  man- 
ner :  — 

1.  By  diminishing  their  surface  tension.  The  fat  be- 
comes separated  into  small  droplets  between  which  the 
fluid  pancreatic  juice  may  penetrate  more  efficiently  than 
around  the  large  oil  drops  of  unemulsified  fat. 

2.  It  dissolves  the  fatty  acids  and  soaps. 

3.  It  holds  the  lipase  of  the  pancreatic  juice  in  solu- 
tion. 

4.  It  acts  as  a  vehicle  to  the  fat  during  its  passage  into 
the  absorbing  epithelial  cells  of  the  intestinal  mucous 
membrane. 

The  Reutilization  of  Bile  Salts  —  During  the  per- 
formance of  these  functions  much  of  the  bile  salts  is 
absorbed  by  the  capillaries  of  the  intestinal  lacteals  and 
carried  by  the  portal  vein  to  the  liver  where  they  are 
again  secreted  as  bile.  Because  of  this,  so  to  speak,  re- 
utilization  of  the  bile  salts  the  work  of  the  liver  in  the 
manufacture  of  bile  is  greatly  economized.  The  liver 
need  only  replace  that  portion  of  the  bile  which  is  de- 
stroyed by  bacteria  in  the  intestinal  canal. 

The  Influence  of  Diet  on  the  Flow  of  Bile  —  A 
meat  diet  stimulates  a  greater  flow  of  bile  than  a  diet  of 
fat,  though  a  meal  of  fat  will  stimulate  a  flow  of  almost 
as  large  a  quantity ;  a  meal  of  carbohydrates  on  the  other 
hand  produces  only  an  insignificant  flow. 

THE    FUNCTIONS    OF   THE   INTESTINAL    JUICE. 

The  Intestinal  Juice  —  The  small  intestine  secretes 
a  juice  called  tlie  succus  entericus.     The  importance  of 

104 


DIGESTION 

this  juice  in  the  digestion  of  food  has  ah'eady  been 
explained,  for  upon  it  depends  the  activity  of  the  pan- 
creatic juice  itself. 

Site  of  Greatest  Digestive  Activity  in  the  Intestines 
—  Secretion  is  much  more  a  function  of  the  upper  por- 
tion of  the  small  intestine  than  of  the  lower  portion. 
The  succus  entericus  secreted  by  the  upper  portion  does 
not  differ  in  quality  but  only  in  amount  from  that  se- 
creted by  the  lower  portion.  The  secretory  power  of 
the  small  intestine  diminishes  progressively  toward  the 
lower  ileum.  On  the  other  hand  the  absorptive  power 
is  increased  from  above  downwards. 

Method  by  which  Secretion  of  Succus  Entericus 
may  be  Studied  —  In  order  to  study  the  mechanism  by 
which  the  succus  entericus  is  secreted,  a  loop  of  intestine 
must  be  isolated  and  made  to  communicate  by  one  or 
both  ends  with  the  skin  surface. 

The  secretion  of  intestinal  juice,  as  is  the  case  with 
pancreatic  juice  and  bile,  begins  within  a  few  minutes 
(ten  minutes  in  the  case  of  intestinal  juice)  after  taking 
a  meal.  The  flow  is  slight  until  two  hours  are  com- 
pleted. During  the  third  hour  it  is  increased  consider- 
ably and  then  gradually  diminishes. 

Nervous  Control  of  the  Secretion  of  Succus  En- 
tericus —  The  intestines  are  supplied  by.  the  vagus  and 
sympathetic  nerves.  It  has  been  repeatedly  confirmed 
that  extirpation  of  the  large  abdominal  plexuses  or  sec- 
tion of  the  splanchnic  nerves  causes  a  diarrhea  which 
lasts  .for  two  or  three  days. 

Is  the  diarrhea  due  to  increased  motor  activity  or  to 
increased  secretion  of  fluid?     After  isolating  three  intes- 

io6 


DIGESTION 

tinal  loops  and  dividing  all  the  nerves  passing  to  middle 
loop,  it  will  be  found  that  the  middle  loop  becomes  dis- 
tended with  intestinal  secretion  which  begins  four  hours 
after  the  operation,  increases  for  twelve  hours  and  then 
rapidly  diminishes. 

In  contrast  to  the  collection  of  fluid  in  this  loop  the 
two  other  end  loops  of  the  series  of  three  are  found 
empt}^ 

Section  of  the  splanchnic  nerves  is  of  course  fol- 
lowed by  vascular  dilatation.  It  is  cjuite  possible  that 
this  increased  blood  supply  may  account  for  the  in- 
creased secretion.  Physiologists,  however,  regard  the 
increased  secretion  after  section  of  the  sympathetic  as 
due  to  the  cessation  of  impulses  inhibitory  to  secretion 
which  normally  are  constantly  flowing  to  the  intestines 
through  these  nerves. 

Certainly  the  influences  of  any  local  nervous  plexuses, 
as  a  cause  of  the  increased  flow  of  intestinal  juice  which 
follows  a  meal,  can  be  excluded,  as  their  connections  are 
divided  in  the  creation  of  an  intestinal  fistula. 

The  Evidence  that  the  Stimulation  of  the  Secretion 
of  Intestinal  Juice  is  Dependent  also  upon  a  Hormone 
—  If  we  exclude  a  reflex  stimulation  through  the  long 
paths  up  the  vagus  to  the  central  nervous  system  and 
down  either  this  nerve  or  the  sympathetic,  as  can  easily 
be  done  by  section  of  the  vagus,  no  other  explanation  of 
the  stimulation  of  intestinal  juice  is  possible  but  one 
which  assumes  the  presence  of  a  hormone. 

Direct  evidence  exists  as  to  its  presence.  The  most 
effectual  stimulant  to  succus  entericus  is  the  presence 
of  pancreatic  juice  in  the  intestine. 

io8 


DIGESTION 

The  injection  of  pancreatic  juice  into  the  blood  stream 
will  not  cause  the  secretion  of  intestinal  juice.  On  the 
other  hand  the  injection  of  secretin  will  cause  a  secretion 
of  intestinal  juice. 

The  same  substance,  secretin,  causes  a  flow  of  the  in- 
testinal juice  and  the  bile.  Evidence,  however,  exists 
that  in  the  intestinal  juice  there  is  not  only  this  secretin, 
which  is  developed  by  the  acid  of  the  chyme,  but  also 
another  secretin,  which  is  present  in  the  pure  alkaline 
intestinal  juice.  The  injection  of  the  pure  intestinal  juice 
from  the  washed  intestines  unacted  upon  by  acid  will 
stimulate  the  secretion  of  succus  entericus  though  it  will 
not  stimulate  the  flow  of  pancreatic  juice. 

The  Influences  of  Mechanical  Stimulation  —  Me- 
chanical stimulation  is  also  efficient,  in  contrast  to  the 
stomach,  in  calling  forth  the  secretion  of  intestinal  juice. 

Within  a  few  minutes  any  solid  body,  as  a  slightly 
distended  rubber  ball,  will  cause  a  flow  of  intestinal  juice. 
It  is  probable  that  the  plexus  of  Meissner  is  responsible 
for  the  flow  of  juice  following  mechanical  stimulation, 
and  transmits  the  stimulus  to  contiguous  portions  of  the 
intestines. 

The  Relation  of  Mechanical  Stimulation  to  the  Pro- 
duction of  Enterokinase  —  It  is  said  that  the  mechan- 
ically stimulated  juice  contains  no  enterokinase  and, 
therefore,  that  the  pancreatic  juice  is  necessary  for  the 
production  of  that  ljod_y  which  activates  it. 

Composition  and  Character  of  Intestinal  Juice  — 
Its  specific  gravity  is  loio.  It  -contains  about  1.5  per 
cent,   solids  of  which  one  half  or  .8  per  cent,   are  in- 


IIO 


DIGESTION 

organic     and     chiefly     sodium    carbonate     and     sodium 
chloride.     Its  ferments  are  — 

1.  Enterokinase,  respo'/isible  for  the  formation  of 
trypsin  from  trypsinogen. 

2.  Erepsin,  a  ferment  which  occurs  not  alone  in  the 
succus  entericus  but  widely  distributed  throughout  the 
body.  It  has  no  digestive  power  on  coagulated  proteins 
or  gelatin.  It  only  slowly  dissolves  caseinogen  and 
fibrin.  Its  characteristic  feature  is  its  power  of  rapidly 
hydrolysing  the  first  products  of  proteolytic  digestion. 

3.  Invertase,  a  ferment  splitting  cane  sugar  into  the 
two  molecules  of  glucose  and  levulose  or  fructose,  of 
which  cane  sugar  is  composed. 

4.  Maltase,  which  splits  maltose  into  the  two  molecules 
of  glucose  of  which  it  is  composed. 

5.  Lactase  which  splits  lactose  into  its  components, 
glucose  and  galactose.  This  ferment  is  present  in  the 
intestinal  juice  of  the  young  of  all  animals  and  through- 
out life  in  those  which  continue  the  milk  diet. 

The  State  in  which  the  Ferments  Exist  in  the  Epi- 
thelial Cells  before  Secretion  —  Erepsin,  maltase,  and 
lactase  probably  exist  as  such  in  the  epithelial  cells  be- 
fore secretion. 

Secretin  exists  as  prosecretin. 

Enterokinase  exists  also  as  a  precursor  within  the  epi- 
thelial cell  before  its  secretion.  The  evidence  for  this 
is  the  fact  that  more  acti\e  solutions  of  enterokinase 
are  to  be  obtained  from  the  cavity  of  the  gut  after  the 
intravascular  injection  of  secretin  than  by  extraction 
from  the  mucous  membrane  scraped  off  from  the  intes- 
tine. 

112 


DIGESTION 

THE    LARGE    INTESTINE. 

Digestion  of  Cellulose  —  The  more  strictly  herbivor- 
ous an  animal  is,  the  longer  its  large  intestine  is  and  the 
more  important  are  its  functions.  In  none  of  the  higher 
mammals  does  cytase,  a  ferment  capable  of  digesting 
cellulose,  exist.  Therefore,  in  the  herbivorous  mammals 
the  cellulose  must  be  dissolved  only  by  the  agency  of 
bacteria.  This  occurs  in  animals  like  the  cow  in  the 
paunch.  In  the  horse  and  rabbit  the  chief  digestion  of 
cellulose  occurs  in  the  caecum. 

The  Relative  Degree  of  Absorption  and  Digestion 
in  the  Large  Intestine  of  Carnivora,  Herbivora  and 
Man  —  In  herbivorous  animals  much  digestion  and  ab- 
sorption occurs  from  the  csecum.  In  carnivora  practi- 
cally all  the  proteins  are  absorbed  before  the  intestinal 
contents  reaches  the  ileocjecal  valve. 

In  man  the  contents  of,  and  processes  occurring  in, 
the  large  intestine  will  vary  with  the  diet.  Under  usual 
conditions  practically  all  the  absorption  of  the  nourish- 
ment occurs  before  the  contents  of  the  intestine  reaches 
the  large  intestine.  If,  however,  much  of  the  food  has 
been  of  green  vegetables  of  coarse  cereals  or  fruits,  a 
large  proportion  of  even  the  digestilDle  nourishment  will 
pass  out  with  the  feces,  though  a  certain  amount  will  be 
absorbed  from  the  large  intestine. 

Secretion  in  the   Large  Intestine  —  The   secreting 
power    of    the    large    intestine    is    negligible.     Even    in 
herbivora  it  is  merely  a  small  amount  of  alkali  carbon- 
ates which  serves  to  neutralize  the  acids  resulting  from 
bacterial  action. 

114 


DIGESTION 

Mucus  is  also  secreted  by  the  membrane  of  the  large 
intestine.  It  aids  in  the  passage  of  the  feces  and  in 
controlling  the  bacterial  growth  in  the  large  gut. 

Amount  and  Character  of  Absorption  from  the 
Large  Intestine  in  Man  —  About  four-fifths  of  the 
fluid  passing  the  ileocsecal  valve  is  absorbed  in  the  large 
intestine.  It  is  almost  solely  the  watery  portion  of  this 
fluid  which  is  absorbed.  For  this  reason  feeding  by 
nutrient  enemata  may  be  regarded  as  only  a  slow  method 
of  starvation.  Some  nourishment  may  be  absorbed  in 
this  manner  moreover  —  after  large  nutrient  enemata 
some  of  the  fluid  may  escape  backwards  through  the 
ileocaecal  valve.  The  isolated  large  intestine  of  man  is 
able  to  absorb  only  about  6  grammes  of  glucose  per  hour 
and  80  c.c.  of  water.  No  absorption  of  egg  albumin  or 
caseinogen  can  be  detected  after  a  considerable  number 
of  hours. 

The  slight  disappearance  of  proteins,  fats  and  carbo- 
hydrates occurring  after  hours  is  probably  due  to  bac- 
terial action. 

The  Excreting  Power  of  the  Large  Intestine  — 
The  large  intestine  performs  an  important  excretory 
function,  and  it  is  a  prominent  channel  by  which  lime, 
magnesium,  iron  and  phosphates  and  the  heavy  metals, 
particularly  those  which  are  toxic,  as  mercury  and  bis- 
muth, leave  the  body. 

MUSCULAR    MOVEMENTS    OF    THE    INTESTINES. 

Methods  of  Study  —  The  movements  of  the  intes- 
tines may  be  studied  by  the  X-ray  method  or  by  direct 
observation  after  opening  the  abdomen. 

116 


DIGESTION 

In  the  latter  case  it  is  necessary  to  protect  the  in- 
testines from  nervous  impulses  which  play  upon  them 
through  nerves  passing  to  them  from  the  cerebro  spinal 
nervous  system  and  the  sympathetic  nervous  system. 
This  can  be  accomplished  by  the  division  of  these  nerves. 

The  intestines  are  then  surrounded  with  a  bath  of 
normal  salt  solution  to  prevent  their  drying  or  being 
effected  by  other  local  external  influences. 

The  intestines  exposed  in  this  manner  will  undergo  two 
kinds  of  movements. 

The  Character  of  the  Movements  ^ — i.  A  swaying 
movement  from  side  to  side. 

2.  Rhythmic  contraction  of  both  the  circular  and  longi- 
tudinal coats  occurring  synchronously  and  repeated 
twelve  to  thirteen  times  per  minute.  These  movements 
may  be  recorded,  without  opening  the  gut,  by  the  entero- 
graph  or  by  inserting  a  thin  rubber  balloon  capable  of 
distention  within  the  lumen  of  the  gut.  The  balloon  is 
connected  with  a  tambour  which  rises  and  falls  as  the 
gut  contracts  upon  it.  Using  this  method  it  will  be  ob- 
served that  the  contractions  are  greatest  over  the  balhjon, 
in  other  words,  at  the  place  where  the  gut  is  exposed  to 
the  greatest  tension. 

Cause  of  Movements  —  These  movements  of  con- 
striction are  due  to  contraction  of  both  coats  and  are 
entirely  myogenetic.  They  are  unaft'ected  ])y  painting 
the  intestine  with  cocaine  or  nicotine. 

Rate  of  Propagation  of  the  Movements  —  They  are 
transmitted  from  fiber  to  fiber  and  j^ass  down  the  in- 
testine at  a  rate  of  5  cm.  per  second. 

Advantages  of  the  X-ray  Method  of  the  Study  of 

118 


DIGESTION 

Intestinal  Movements  and  their  Character  as  so 
Studied  —  The  X-ray  method  enables  one  to  study  more 
accurately  what  occurs  under  the  conditions  under  which 
the  intestines  functionate  normally.  Using  this  method 
the  food  column  can  be  seen  to  form  a  cylindrical  column 
within  the  intestines.  By  contractions  of  the  gut,  con- 
strictions occur  which  divide  the  column  into  segments. 

Each  of  these  segments  are  halved  within  a  few 
seconds  by  other  constrictions  occurring  between  the 
places  where  the  first  set  of  constrictions  took  place. 
When  the  segment  is  halved,  the  first  constriction  passes 
off,  so  that  a  new  segment  is  formed  with  its  extremities 
at  the  mid  points  of  the  first  series  of  segments.  Again 
after  a  few  seconds  these  new  segments  are  halved  by 
constrictions  dividing  them  at  the  place  of  the  first  set 
of  contractions. 

If  these  contractions  are  propagated  as  a  continuous 
wave,  other  contractions  are  superadded,  transforming 
the  intestinal  segments  into  spherical  or  oval  segments. 
The  process  of  halving  the  segments  depends  upon  the 
fact  that  the  center  of  each  segment  between  two  con- 
stricted portions  is  subjected  to  the  stimulus  of  the  great- 
est increase  in  tension. 

None  of  these  movements  results  in  an  onward  propa- 
gation of  the  food.  They  simply  serve  to  mix  thor- 
oughly the  intestinal  contents  and  to  bring  it  all  into 
contact  with  the  intestinal  wall. 

The  onward  propagation  of  the  food  can  only  be  ac- 
compHshed  by  a  true  peristalsis.  True  peristalsis  in- 
volves the  passage  in  one  direction  of  a  wave  of  contrac- 
tion preceded  by  a  wave  of  relaxation. 

1 20 


DIGESTION 

The  Character  of  True  Peristalsis  and  the  Mechan- 
ism upon  which  it  Depends  in  the  Intestine  —  The 

Local  Nervous  Mechaiiisiii  —  The  difference  between 
true  peristalsis  and  the  kneading  movements,  which  have 
been  described,  may  be  ilkistrated  by  stimulating"  a  seg- 
ment of  gut  locally  into  whicli  a  slightly  distended  rubber 
balloon  has  been  inserted.  If  the  gut  is  pinched  one  half 
an  inch  below  the  balloon,  there  will  be  a  strong  contrac- 
tion over  the  balloon.  If  it  is  pinched  above  the  balloon 
there  will  be  a  relaxation  at  the  balloon. 

Local  stimulation,  therefore,  causes  relaxation  below 
the  stimulated  point  upon  any  contents  distending  it  and 
contraction  above.  This  double  effect  results  in  the  slow 
passage  onward  of  the  contents  of  the  intestine  for  its 
whole  length.  It  depends  upon  the  local  nervous 
mechanism  within  the  intestinal  walls;  the  plexus  of 
Auerbach. 

Painting  the  intestines  with  nicotine  or  cocaine  abol- 
ishes these  peristaltic  contractions.  On  the  other  hand, 
division  of  all  the  connections  between  the  gut  and  the 
brain  or  spinal  cord  does  not  abolish  them. 

Peristalsis  in  a  direction  the  reverse  of  the  aboral 
direction  does  not  occur  in  the  small  intestine.  Even 
when  a  segment  of  the  small  intestine  is  reversed  by 
dividing  it  off  and  resuturing  it  in  the  opposite  direction 
so  that  the  continuity  of  the  gut  is  restored  a  species  of 
intestinal  obstruction  will  result.  An  axial  reflux  of  in- 
testinal contents  above  such  an  obstructed  portion  is,  how- 
ever, possible. 

The  Control  of  the  Intestinal  Movements  by 
Causes  Acting  through  the  Central  Nervous  System 

122 


DIGESTION 

from  within  —  Though  the  local  nervous  mechanism  of 
the  intestine  is  alone  the  essential  causative  factor  in  the 
peristaltic  movements  of  the  guts  from  local  stimulation, 
yet  the  movements  of  the  intestines  are  subject  to  the 
control  of  the  central  nervous  system. 

Impulses  passing  to  the  intestine  along  the  vagus  nerve 
produce  an  initial  inhibition  of  the  whole  small  intestine, 
followed  by  increased  irritability  and  increased  contrac- 
tion. 

Splanchnic  impulses  cause  complete  relaxation  of  both 
coats  of  the  small  intestine.  Both  these  effects,  i.e.,  both 
vagal  and  sympathetic  effects,  may  be  reproduced  by 
electrical  stimulation  of  these  nerves. 

Normally  there  descends  through  the  splanchnic  con- 
stant or  tonic  inhibitory  impulses.  The  mere  opening 
of  the  abdomen  is  sufficient  to  greatly  increase  these  in- 
hibitory impulses  so  that  the  division  of  the  splanchnic 
is  essential  to  the  study  of  the  movements  of  the  in- 
testines through  the  opened  abdomen. 

The  Control  of  the  Ileo  Colic  Sphincter  —  The  cir- 
cular fibers  of  the  lowest  two  cm.  of  the  ileum  are  thick- 
ened into  a  sphincter  like  structure  called  the  ileo  colic 
sphincter.  It  relaxes  to  permit  the  passage  of  intestinal 
contents  pressing  upon  it  from  above,  but  contracts 
against  the  pressure  of  contents  from  below. 

Stimulation  of  the  vagus  does  not  effect  the  ileo  colic 
sphincter,  but  while  stimulation  of  the  splanchnic  causes 
relaxation  of  the  rest  of  the  intestine,  it  causes  contrac- 
tion of  the  ileo  colic  sphincter. 


124 


DIGESTION 


MOVEMENTS    OF   THE  LARGE   INTESTINES. 

Difference  in  Function  and  Length  of  Large  In- 
testine in  Omnivora,  Herbivora  and  Carnivora  —  In 

man  the  contents  of  the  large  intestine  are  considerable. 
In  herbivora  they  are  still  greater  and  the  digestive  and 
absorptive  processes  taking  place  in  the  large  intestine 
very  extensive.  In  carnivora  the  functions  of  the  large 
intestine  are  almost  entirely  propulsive. 

Inasmuch  as  whatever  absorption  and  digestion  takes 
place  in  the  large  intestine  chiefly  takes  place  in  the 
caecum,  propulsion  occurs  in  the  sigmoid  and  rectum. 
The  transverse  colon  participates  in  digestion  and  absorp- 
tion but  to  a  less  degree  than  the  c?ecum  and  ascending 
colon.  The  descending  colon  may  be  considered  inter- 
mediate in  its  function.  Carnivora  possess  practically 
only  the  distal  portion  of  the  large  intestine. 

Nature  and  Effects  Produced  by  Contraction  of 
Large  Intestines  —  The  X-ray  method  has  furnished 
valuable  information  upon  the  movements  of  the  large 
intestine.  As  the  caecum  receives  the  food  from  the 
ileum,  waves  of  contraction  occur  within  it. 

They  begin  at  the  juncture  between  the  transverse  and 
ascending  colon  and  travel  backward  toward  the  caecum. 

They  follow  each  other  so  rapidly  that  se\'eral  may  be 
present  at  one  time.  They  should  not  be  described  as 
true  antiperistaltic  waves,  as  they  are  not  preceded  by  an 
advancing  wave  of  inhibition. 

They  nevertheless  do  force  the  food  backwards 
against  the  ileo  colic  valve,  which,   with  the  ileo  colic 


126 


DIGESTION 

sphincter,  is  efficient  in  preventing  the  fluid  from  reenter- 
ing the  ileum. 

.  Inasmuch  as  the  whole  contents  cannot  be  contained 
within  the  caecum  a  certain  portion  will  slip  in  the  re- 
verse direction  toward  the  transverse  colon  as  an  axial 
stream.  The  forcing  of  the  contents  of  the  ascending 
colon  into  the  caecum  stimulates  in  the  latter  a  true  peris- 
taltic wave  beginning  in  the  caecum  and  traveling  to- 
ward the  transverse  colon. 

At  first  these  waves  are  not  very  pronounced  and  die 
away  before  they  have  travelled  far.  Movements  of  this 
character  result  in  a  thorough  kneading  and  retention  of 
the  intestinal  contents  within  the  caecum  and  ascending 
colon.  Every  opportunity  is  afforded  which  is  favorable 
to  absorption  from  the  colon.  The  total  result  of  the 
process  is  the  absorption  of  water  from  the  intestinal  con- 
tents. 

The  Propulsive  Mechanism  of  the  Large  Intestine 
—  As  more  and  more  contents  are  forced  into  the  colon 
from  the  ileum,  the  more  solid  portions  collect  in  the 
descending  colon  where  they  are  separated  from  the  more 
fluid  portions  in  the  transverse  colon  by  transverse  con- 
strictions and  by  the  fluid  of  the  splenic  flexure. 

By  means  of  true  peristalsis  in  the  descending  colon 
these  masses  are  driven  onward  in  the  descending  colon. 
In  this  portion  of  the  large  intestine  antiperistalsis  does 
not  occur.  The  descending  colon  is,  therefore,  the  inter- 
mediate portion  of  the  large  intestines  where  propulsive 
peristalsis  is  the  chief  activity.  It  never  becomes  dis- 
tended because  it  possesses  a  very  sensitive  irritability 


128 


DIGESTION 

to  any   distending   force   from   within.     It  may  be   re- 
garded as  a  transferring  segment. 

The  Physiology  of  Defecation  —  The  next  segment 
of  the  large  intestine,  the  sigmoid  flexure,  may  be  re- 
garded as  the  collecting  place  for  the  large  intestine. 
The  large  intestine  receives  nerves  from  the  sympathetic 
system  through  the  inferior  mesenteric  plexus  and  its 
more  distal  portion  directly  from  the  sacral  region  of 
the  cord  through  the  pelvic  visceral  nerves,  the  nervi 
erigentes.  The  mechanism  and  control  of  the  movements 
of  the  large  intestine  is  largely  of  the  same  nature  as 
in  the  small  intestine. 

When  the  local  distention  of  the  sigmoid  becomes 
strong  enough  to  excite  contractions,  the  sigmoid  empties 
itself  into  the  rectum.  The  distinguishing  characteristic 
of  the  movements  of  its  more  distal  portion  especially 
the  rectum  is  its  subordination  to  the  central  nervous 
system.  It  receives  nerves  through  the  pel\ic  visceral 
nerves.  It  remains  iiiacti\e  until  that  degree  of  disten- 
tion is  obtained  which  is  capable  of  reflexly  exciting 
efferent  impulses  in  these  pelvic  visceral  nerves. 

Stimulation  of  these  nerves  result  in  a  shortening  of 
this  portion  of  the  gut  which  is  produced  by  a  contraction 
in  part  of  the  longitudinal  coat.  These  contractions  are 
.  followed  by  a  contraction  of  the  circular  muscular  coat. 
The  afferent  impulses  excited  by  the  i)resence  of  feces  in 
the  rectum  excite  afferent  impulses  which  reach  conscious- 
ness creating  there  impressions  which  produce  the  desire 
to  defecate. 

The  act  of  defecation  is  only  in  part  voluntary  and 
dependent  on  pressure  which  produces  the  desire  to  defe- 

130 


DIGESTION 

cate.  The  act  of  defecation  is  assisted  or  inaitgnrated  by 
the  voluntary  pressure  of  the  abdominal  muscles  raising 
the  pelvic  floor  and  forcible  contraction  of  the  levator  and 
coccygeus  muscle. 

The  act  may,  therefore,  be  in  part  voluntary,  but  for 
its  completion  the  integrity  of  a  nervous  center  in  the 
lumbar  portion  of  the  spinal  cord  is  essential. 

Through  synapses  and  nerve  cells  in  this  portion  of  the 
spinal  cord  and  in  response  to  an  intrarectal  pressure  in 
man  of  30  to  40  m.m.  of  Hg.,  efferent  impulses  descend 
the  pelvic  visceral  nerves  which  cause  a  contraction  of  the 
longitudinal  and  later  the  circular  fibers  of  the  recti,  as- 
sisted by  contraction  of  the  coccygeus  and  levator  ani 
muscles,  and  at  the  same  time  by  an  inhibition  of  the 
sphincter  ani. 

All  these  contractions,  accompanied  by  the  inhibition  of 
the  sphincter  and  by  the  voluntary  muscles  of  the  ab- 
domen, occur  with  a  proper  coordination.  The  coordina- 
tion depends  upon  the  connections  of  the  nerve  cells  in 
the  lumbar  region  of  the  spinal  cord.  The  action  of  these 
cells  may  be  inhibited  or  augmented  by  local  stimuli,  such 
as  cold  or  heat,  or  by  stimuli  from  the  higher  portions 
of  the  nervous  system  such  as  fear  or  various  emotions. 

Absorption  of  the  Products  of  Digestion  from  Ali- 
mentary Canal  —  The  Absorption  of  Water  —  The  in- 
take of  water  seems  to  be  regulated  largely  by  the  cen- 
tral nervous,  system,  any  deficiency  of  water  in  the  blood 
being  felt  as  an  intense  thirst.  This  factor,  however,  only 
creates  the  need  of  the  ingestion  of  water.  The  ab- 
sorption of  water  from  the  alimentary  canal  is  a  dift'erent 
matter.     The    amount    absorbed    is    entirely    dependent 

132 


•    DIGESTION 

upon  the  amount  ingested  and  not  upon  the  state  of  de- 
pletion of  the  blood  of  its  watery  constituents. 

Irrespective  of  the  amount  of  water  ingested  it  is  prac- 
tically impossible  to  provoke  watery  motions  from  the 
bowels.  Nevertheless  the  amount  of  water  in  the  blood 
remains  constant,  no  matter  whether  an  individual  drinks 
one  or  six  liters  a  day.  In  other  words  any  excess  of  the 
excessive  amount  which  is  absorbed  is  excreted  almost 
immediately  by  the  kidneys. 

Practically  no  water  is  absorbed  by  the  stomach. 
Water  received  into  an  empty  stomach  quickly  passes  into 
the  duodenum. 

Probably  when  large  quantities  of  water  are  drunk 
with  the  meals,  greatly  diluting  the  gastric  contents,  it 
passes  quickly  into  the  duodenum. 

It  thus  not  only  interferes  with  the  gastric  digestion 
but  also  with  the  normal  mechanism  for  the  excitation  and 
activation  of  the  pancreatic  juice. 

In  such  conditions  as  stenosis  of  the  pylorus  the  pa- 
tients die  rather  of  water  starvation  than  of  food  starva- 
tion. 

The  Relative  Amount  of  Absorption  from  the  In- 
testines —  The  chief  absorption  of  water  occurs  from  the 
small  intestine.  Notwithstanding  the  failure  of  the  ab- 
sorption of  water  from  the  stomach  and  its  almost  entire 
absorption  in  the  intestines  the  contents  of  the  lower 
ileum  are  about  as  fluid  as  that  of  the  duodenum  and  iiv 
quantity  amount  to  only  about  as  much  as  the  digestive 
fluids  secreted  by  the  various  digestive  glands  draining 
into  the  small  intestine. 

The  Absorptive  Mechanism  of  the  Intestinal  Sur- 

134 


DIGESTION 

face  —  The  surface  of  the  small  intestine  is  increas'fed. 
three  to  twelve  times  by  closely  set  finger-like  projections, 
invisible  to  the  naked  eye,  which  protrude  from  the  folds 
of  the  intestine. 

These  are  called  villi.  Each  villus  is  lined  by  a  co- 
lumnar layer  of  epithelial  cells  resting  upon  an  incom- 
plete basement  membrane. 

The  form  of  the  villus  is  maintained  by  reticular  con- 
nective tissue  and  a  central  lymphatic  stem,  ending  to- 
ward the  interior  of  the  gut  in  an  enlarged  club-like 
extremity. 

This  central  lymphatic  stem  is  called  a  lacteal.  Sur- 
rounding it  is  a  vascular  network  of  capillaries  which  are 
branches  of  an  efferent  arteriole  and  efferent  venule. 

The  central  lacteal,  which  is  lined  with  delicate  en- 
dothelial walls,  drains  into  a  plexus  of  lymphatics  at 
the  base  of  the  villus  and  communicates  with  other 
lymphatics  and  drain  eventually  into  the  cisterna  lym- 
phaticus  magna,  and  thence,  by  the  thoracic  duct,  its  con- 
tents open  into  the  venous  circulation  at  the  juncture  of 
the  subclavian  and  internal  jugular  vein.  The  venules  of 
the  villi  drain  into  the  portal  vein  and  by  this  vein  pass 
to  the  liver.  The  meshes  of  the  areolar  connective  tissue 
filling  the  villus  are  filled  with  many  lymph  cells  and 
leucocytes.  All  the  structures  of  the  villus,  including  the 
lymphatics  plexus  at  its  base,  are  superficial  to  the  mus- 
cularis  mucosae,  but  muscular  fibers  extend  up  from  the 
muscularis  mucosae  into  the  villus  and  aid  by  their  con- 
traction the  lymph  flow  from  the  villus. 

The  Rate  of  Flow  of  Chyle  —  Even  during  rest  of 
the  animal  there  is  a  constant  flow  of  lymph,  varying 

13^^ 


DIGESTION 

from   I  to  lo  c.c.  in  ten  minutes,  through  the  thoracic 
duct. 

THE    ABSORPTION    OF    WATER    AND    SALTS. 

Can  the  Absorption  of  Salt  Solution  be  explained 
as  a  Process  of  Filtration  or  Osmosis?  —  The  circula- 
tion through  the  vascular  system,  i.e.,  the  capillaries  of 
the  villus,  is  very  rapid  and  it  must  be  remembered  at  a 
comparatively  high  pressure,  at  least  30  m.m.  of  Hg. 

No  absorption,  therefore,  from  tlie  interior  of  the  gut 
into  the  blood  within  the  capillaries  could  occur  by  a 
simple  process  of  filtration.  What  now  is  the  explana- 
tion of  the  absorptions  of  the  water  and  salts  of  solutions' 
from  the  interior  of  fhe  intestine  into  the  flood  stream? 

1 .  It  cannot  be  a  simple  process  of  filtration,  as  the 
blood  pressure  is  too  high  in  the  capillaries. 

2.  It  cannot  be  due  to  osmotic  pressure,  even  though 
absorption  may  be  regulated  by  osmotic  pressure. 

A  solution  of  normal  salt  exactly  isotonic  with  the 
blood  is  absorbed  completely  from  the  interior  of  an  in- 
testinal loop.  More  than  this  both  a  hypo-  and  hyper- 
tonic solution  of  salt  is  absorbed  from  an  intestinal  loop, 
though  the  former  is  absorbed  a  little  more  slowly  than 
the  latter. 

The  solutions  of  the  monosaccharides,  glucose  and 
fructose,  are  absorbed  from  the  intestine  while  in  the 
absence  of  the  hydrolytic  ferments  cane  sugar  and  maltose 
and  lactose  are  not  absorbed  at  all.  The  rates  and 
possibilities  of  absorption  are,  therefore,  cjuite  apart  from 
the  normal  rates  of  diffusion  of  these  substances. 

Idle  most  significant  fact,  however,  concerns  the  ab- 

>3S 


DIGESTION 

sorption  of  an  animal's  own  serum.  When  injected 
within  a  loop  of  intestine  it  undergoes  absorption  com- 
pletely. It  becomes,  however,  in  the  later  stages  of  its 
absorption  somewhat  more  concentrated.  It  is  impos- 
sible to  explain  the  absorption  of  such  a  serum  with  its 
contained  water  and  salts  by  a  process  of  the  diffusion  of 
a  digested  albumin,  since  the  absorption  of  the  serum 
occurs  even  if  the  intestinal  loop  into  which  the  serum 
is  injected  is  washed  perfectly  free  of  trypsin.  More- 
over, the  serum  itself  is  strongly  antitryptic. 

It  must  be  concluded  that  the  passage  of  water  and  salts 
and  also  of  certain  other  substances  from  the  interior  of 
the  intestines  is  determined  solely  by  the  epithelial  cells 
themselves;  in  other  words  by  their  nutritional  needs  for 
the  substances  held  in  solution  by  the  fluids  and  salts 
absorbed.  It  is  a  manifestation  of  their  own  activity. 
Further  evidence  supporting  this  view  is  the  fact  that 
any  injury  to  these  cells  diminishes  their  absorptive 
powers.  As  important  constituents  of  these  cells,  and 
particularly  we  may  assume  of  their  free  borders,  must 
be  reckoned  lecithin  and  cholesterin. 

These  are  lipoid  substances  presenting  many  semidif- 
fusible  properties.  In  their  solubilities  and  misabilities 
they  stand  related  to  both  the  fats  and  water.  We  can 
conceive  of  these  substances,  therefore,  as  forming,  so 
to  speak,  the  chemical  defenses  of  the  cells  against  sub- 
stances harmful  or  of  no  use  to  the  cell. 

We  must  not  forget  that  the  cement  substance  between 
the  cells  may  be  permeable  to  some  substances. 


140 


DIGESTION 


THE    ABSORPTION    OF    FATS. 


The  Power  of  all  Cells  to  Dispose  of  Fat  —  Every 
cell  in  the  body  can  utilize  fat ;  can  ingest  it,  store  it  up 
or  hydrolyze  it  and  ultimately  oxidize  it  completely  for 
the  purpose  of  supplying  energy  for  its  own  activites. 
Fat  may,  therefore,  enter  the  circulation  as  such  and  be 
thus  transported  to  those  cells  by  which  it  is  to  be  utilized. 

Within  the  intestine  the  greater  portion  of  the  fats 
exist  as  fatty  acids  and  soaps.  The  proportion  of  these 
substances  increases  as  the  ileo  csecal  valve  is  approached. 

Proportion  of  Fat  which  is  Digested  —  About  5  per 
cent,  of  the  fat  ingested,  even  from  a  meal  fairly  rich  in 
fat,  escapes  hydrolysis  in  its  passage  through  the  in- 
testine. By  what  path  now  does  the  fat  reach  the  blood 
stream  and  the  tissues  ? 

Proportion  of  Fat  Entering  the  Blood  Stream  by 
the  Thoracic  Duct  —  At  least  60  per  cent,  of  the  fat 
enters  the  blood  stream  as  such  by  way  of  the  thoracic 
duct. 

Ligature  of  the  thoracic  duct  diminishes  the  absorp- 
tion of  fat  but  does  not  abolish  it.  Sixty  per  cent,  only  of 
the  fat  which  disappears  from  the  intestines  can  be  col- 
lected in  the  thoracic  duct. 

How  does  the  Remainder  Reach  the  Circulation?  — 
i\fter  ligature  of  the  thoracic  duct,  the  percentage  of  fat 
in  the  blood  falls  to  a  minimum  and  this  minimum  is  not 
raised  l)y  giving  a  meal  rich  in  fat,  though  a  considerable 
portion  disappears  from  the  intestines.  It  is  not  known 
how  this  minimum  exists  in  the  blood  nor  how  it  gets 


142 


DIGESTION 

there.  It  certainly  does  not  circulate  in  the  blood  as 
soap  for  soap  is  a  severe  poison.  Perhaps  the  cells  of 
the  body  use  the  fat  as  rapidly  as  it  can  be  supplied  so 
that  any  hint  as  to  its  existence  in  the  blood  is  difficult  of 
recognition. 

The  Histological  Evidence  on  the  Absorption  of 
Fat  —  Alicroscopical  examination  of  the  villi  during  the 
absorption  of  fat  by  the  epithelial  cells  discloses  the  pres- 
ence of  fat  droplets  easily  recognizable  within  the  cells. 
They  take  an  intense  black  stain  with  osmic  acid  or  a 
characteristic  red  stain  by  alkaline  or  sudan  red.  During 
the  early  stages  of  fat  absorption  numerous  small  droplets 
are  found  in  the  cells,  which  increase  in  size  till  the  cells 
become  actually  filled  with  fat.  Near  the  base  of  the 
cells  the  fat  is  found  in  the  intercellular  spaces  between 
the  cells.  We  may  conclude,  therefore,  that  the  fat  enters 
the  epithelial  cell  as  soap  or  fatty  acid,  is  resynthesized  in 
the  cell  into  fat  and  becomes  extruded  from  the  other 
end  of  the  cell.  Sixty  per  cent,  of  it  then  reaches  the 
lymphatics  which  stand  out  as  numerous  white  lines  in  the 
intestinal  wall  and  in  the  mesentery. 

By  these  the  fat  reaches  the  thoracic  duct,  the  contents 
of  which  show  a  distinct  change  from  the  increase  in  the 
content  of  fat.  The  chyle  may  contain  as  much  as  6  per 
cent.,  and  12  grams  per  hour  may  be  transported  through 
the  duct  in  the  course  of  an  hour  in  a  moderate  sized  dog. 

The  contractions  of  the  muscular  elements  of  the  villus 
assist  materially  in  emptying  the  lacteals  and  thus  start- 
ing the  flow. 

The   Evidence   that   Fat   Enters   the   Cells   in  the 


144 


DIGESTION 

Hydrolyzed  Form  —  The  following  facts  confirm  the  be- 
lief that  the  fats  enter  the  epithelial  cells  in  its  hydrolyzed 
form. 

1.  Bile  is  a  solvent  of  the  fatty  acid  and  soaps,  but 
only  emulsifies  neutral  fats. 

2.  The  presence  of  bile  in  the  intestine  is  essential  for 
the  normal  absorption  of  fat.  After  a  biliary  fistula  the 
absorption  of  fat  sinks  from  98  to  40  per  cent.  The  un- 
absorbed  residue  appears  in  the  feces  and  by  coating"  the 
other  food  stuffs  prevents  their  absorption. 

3.  Ligature  of  the  pancreatic  duct  prevents  all  lipoly- 
sis  except  that  occurring  in  the  stomach  and  due  to  micro- 
organisms. This  operation  very  seriously  diminished  the 
amount  of  fat  absorbed. 

4.  Substances  almost  identical  with  fat  from  a  physical 
standpoint,  such  as  petroleum  or  parafifin,  are  not  ab- 
sorbed when  introduced  into  the  intestine  in  the  state  of 
fine  emulsion,  the  intestinal  cells  pick  up  the  fat  but  re- 
ject the  paraffin  petroleum. 

Normally  95  per  cent,  of  the  fat  is  absorbed  in  its  pas- 
sage through  the  small  intestine.  Six  per  cent,  enters  the 
thoracic  duct  and  40  per  cent,  reaches  the  blood  in  a  way 
as  yet  unknown. 

TPIE    ABSORPTION    01-"    CAKHOI I  YDKATIiS. 

Absorption  of  Carbohydrates  is  by  the  Capillary 
Circulation  of  the  Villus  —  The  lymi)li  from  the  tho- 
racic duct  contains  no  more  carboh^ydrates  than  does  tlie 
blood. 

Several  (observers  ha\'e  demonstrated  that  after  a  large 
meal  of  carbohydrates  a  larger  percentage  exists  in  the 

146 


DIGESTION 

blood  of  the  portal  vein  than  in  the  blood  of  the  systemic 
circulation. 

These  two  facts  prove  that  carbohydrates,  like  salts  and 
water,  are  absorbed  by  the  capillary  circulation  in  the 
villi.  We  must  never  lose  sight  of  the  fact  that  only  the 
monosaccharides  —  manose,  fructose,  glucose  and  galac- 
tose —  can  be  absorbed  and  utilized  by  the  body. 

Other  sugars  when  injected  into  the  blood,  with  the 
exception  perhaps  of  maltose,  are  excreted  quantitatively 
in  the  urine.  Maltose  forms  an  exception  because  of  the 
universal  presence  of  maltase. 

ABSORPTION    OF    PROTEINS. 

The  Route  (Capillary  Circulation  of  the  Villus)  by 
which  the  Proteins  are  Absorbed  —  Evidence  from  Ex- 
periments on  the  Thoracic  Duct  —  There  is  no  variation 
in  the  lymph  flow  or  in  the  amount  of  proteins  which  it 
contains,  as  a  result  of  digestion. 

a.  Ligature  of  the  thoracic  duct  does  not  interfere  with 
the  absorption  of  proteins.  One  of  the  normal  con- 
sequences of  the  absorption  of  proteins  is  an  increase  in 
the  amount  of  urea  excreted  by  the  kidney. 

Ligature  of  the  thoracic  duct  does  not  diminish  the 
secretion  of  urea  following  protein  absorption. 

We  may  conclude,  therefore,  first  that  the  absorbed 
protein  does  not  reach  the  blood  stream  by  way  of  the 
lymph  circulation  but  rather  directly  by  way  of  the  capil- 
lary circulation  of  the  villi. 

b.  Histological  Evidence  —  Definite  changes  have  been 
identified  in  the  epithelial  cells  during  protein  absorption. 
They  become  swollen,  stain  less  deeply  and  their  basal 

148 


■  DIGESTION 

ends  are  not  so  well  defined.     Their  protoplasm  seems  to 
become  distended  with  a  hyaline  coagulable  material. 

As  a  second  conclusion  we  may  assign  to  the  epithelial 
cells  the  function  of  being  the  active  agents  in  the  ab- 
sorption of  proteins. 

The  next  question  concerns  the  chemical  condition  to 
which  proteins  may  be  reduced  during  absorption. 

Chemical  Condition  in  which  Proteins  are  Absorbed 
—  There  seems  to  be  some  evidence  that  protein  may  be 
absorbed  without  having  undergone  any  hydration  what- 
ever. For  instance  21  per  cent,  of  egg  or  serum  albumin 
has  been  absorbed  from  loops  of  intestine  washed  free 
of  ferments  in  three  hours'  time. 

During  the  same  period  69  per  cent,  of  alkali  albumin 
has  disappeared.  By  contrast  no  absorption  of  syntonin 
or  casein  has  been  observed. 

These  absorbed  albumins,  however,  have  failed  to  ex- 
cite the  production  of  specific  precipitins  in  the  serum  of 
such  an  animal. 

'  This  fact  is  pretty  good  evidence  that  the  proteins  did 
not  pass  unchanged  through  the  intestinal  wall. 

Is  it  possible  that  intercellular  digestion  could  occur  ? 
In  whate\'er  way  these  questions  may  be  ans\\'ered  the 
absorption  of  unchanged  proteins  plays  a  small  part  in 
the  absorption  of  proteins  from  the  alimentar)'  canal. 
Most  of  our  protein  is  ingested  in  an  insoluble  coagulated 
form.  ■  . 

The  proteoses  and  peptones  are  dififusible  but  they 
cannot  pass  into  the  blood  as  such  because,  injected  into 
the  blood  .stream,  they  are  very  toxic,  even  in  small  (|uan- 
tities  causing  death. 

150 


DIGESTION 

No  trace  of  albnmose  or  peptone  is  found  in  the 
blood  of  the  portal  vein  during  the  digestion  of  proteins. 

Attempts  have  been  made  to  prove  that  the  peptone 
found  within  the  intestinal  mucous  membrane  itself  of  an 
excised  loop,  immediately  after  the  rapid  coagulation  of 
the  latter,  undergoes  a  reconstruction  into  protein  within 
the  membrane  if  the  membrane  of  the  experimental  loop 
is  kept  alive  by  an  artificial  circulation  half  an  hour  be- 
fore its  rapid  coagulation,  because  under  these  conditions 
there  is  a  disappearance  of  the  peptone  from  the  interior 
of  the  loop.  Its  disappearance,  however,  is  to  be  at- 
tributed rather  to  a  rapid  hydrolysis  by  the  erepsin  which 
it  contains.  Moreover  the  epithelial  elements  of  such  a 
membrane  cannot  be  kept  alive  by  such  a  method  of 
artificial  circulation.  After  one  hour's  time  there  is  no 
increase  in  the  coagulable  proteins  within  the  mucous 
membrane  of  such  an  experimental  loop. 

On  the  other  hand  it  is  possible  to  keep  animals  alive 
on  amino  acids  or  the  ultimate  products  of  pancreatic 
chgestion  alone. 

Further  than  this  certain  observers  have  detected  an 
increase  of  the  amino  acids,  at  least  of  the  protein  nitro- 
gen, in  the  blood  of  the  portal  vein  after  meals  rich  in 
protein. 

It  is  possible  also  to  extract  leucin  from  the  mucous  ■ 
membrane  of  an  intestine,  although  not  directly,  yet  after 
treating  the  membrane  with  acid.  This  fact  indicates 
that  leucin  was  present  in  an  easily  disassociable  condition. 
Unquestionably  a  further  breaking  down  of  protein  than 
even  the  amino  acids  stage  occurs  during  the  process  of 
its  passage  into  the  portal  blood. 

152 


DIGESTION 

All  physiologists  agree  that  there  is  an  increase  in  the 
ammonia  of  the  blood  in  the  portal  circulation.  There- 
fore in  the  wall  of  the  gut  there  must  be  a  complete 
(leamination  of  a  portion  of  the  amino  acids.  The  am- 
monia thus  formed  passes  to  the  liver  and  is  there  trans- 
formed into  urea. 

The  Facts  Relative  to  the  Non-Nitrogenous  Portion 
—  The  above  discussions  leaves  us  still  to  account  for  the 
non-nitrogenous  portion  of  the  protein  molecule.  It 
seems  to  be  oxidized  very  rapidly,  for  it  produces  no  in- 
crease in  the  body's  store  of  fat  but  rather  an  increase  of 
the  output  of  CO2  and  the  respiratory  exchange  of 
oxygen. 

We  may  conclude,  finally  that,  while  proteins  are  prob- 
ably in  large  part  absorbed  as  amino  acids  or  at  any  rate 
are  passed  on  in  this  hydrolyzed  form  to  the  blood,  they 
are  also  passed  on  in  the  still  more  completely  broken  up 
form  of  ammonia. 

We  must  also  remember  that  it  may  still  be  possible 
for  a  certain  synthesis  of  amino  acids  to  occur  in  the 
epithelial  cells  during  the  passage  of  the  protein  on  to  the 
Ijlood  as  reformed  coagulable  proteins;  and  thirdly  that 
neither  of  these  assumptions  would  entirely  negate  the 
direct  absorption  of  coagulable  proteins.  It  is  possible, 
therefore,  that  proteins  may  l^e  absorbed  in  all  three  of 
these  ways. 


f54 


LECTURE  NOTES  ON 
PHYSIOLOGY 


BY 
HENRY  H.  JANEWAY,  M.D. 


THE  NERVOUS  SYSTEM 


NEW  YORK 

PAUL    B.    HOEBER 

67-69  EAST  59TH  STREET 


Copyright,  1915,   , 
By  PAUL  B.  HOEBER 


Reprinted  October,  1917,  and  Oclober^,  igi8 


I 
THE  NERVES 

THE  PERIPHERAL  NERVES 

STRUCTURAL   BASIS   OF    THE    NERVOUS   SYSTEM 

The  Purpose  Served  by  the  Nervous  System — The  nervous 
system  has  developed  in  order  that  a  rapid  communication  be- 
tween the  distant  portions  of  the  body  may  be  possible.  Its  tis- 
sues in  the  process  of  specialization  of  function  have  acquired  the 
highest  perfection  of  the  vital  phenomena  of  excitability  and  of  the 
power  of  transmission  of  a  change  dependent  on  excitement. 
Among  unicellular  animals  special  provision  for  such  a  means  of 
communication  does  not  exist.  Among  the  metazoa,  i.e.,  the  sponges, 
no  evidence  of  a  nervous  system  exists.  It  is  in  the  Ccelenterata 
that  the  first  evidences  of  a  nervous  system  are  met  with. 

DEVELOPMENT   OF    THE    NERVOUS   SYSTEM 

The  Hydra  —  In  the  hydra  some  of  the  epithelial  cells  have  pro- 
longations which  join  or,  at  least,  come  into  contact  with  deeper 
cells  possessing  special  contractile  power.  (Fig.  1.)  We  can  imag- 
ine that  these  epithelial  cells  with  their  prolongations  have  become 
endowed  with  a  special  sensitiveness  to  external  irritants,  and  pos- 
sess the  power  of  quickly  transmitting  the  effects  of  the  external 
changes  upon  it  to  the  contractile  cells  and  in  a  manner  to  cause  the 
latter  to  respond  immediately. 

Ccelenterates  —  The  jelly  fish  presents  quite  an  advance  over  this 
simple  nervous  system  and  no  intermediate  stages  are  known. 
(Fig.  2.)  The  nervous  system  of  the  jelly  fish  is  limited  to  the 
region  beneath  the  margin  of  the  umbrella.  From  the  epithelium 
of  the  surface,  fibers  pass  inward  forming  a  network  around  the 
margins  of  the  umbrella.  In  this  network  there  are  thickenings 
in  which  are  situated  nerve  cells.     (Fig.  3.)     A  finer  network  of 

4 


THE  NERVOUS  SYSTEM 


Fig.  1.— Diagrammatic  illustration  of  the  evolution  of  the  reflex  arc. 
A  shows  a  single  cell  differentiated  into  a  conductive  (1),  and  contractile 
portion  (2).  In  B  the  conductive  portion  (1)  and  the  contractile  portion  (2) 
exist  as  separate  cells  and  maiatain  their  connection  with  the  sensory  element 
by  a  slender  conductive  portion  in  this  cell,  which  represents  a  nerve  (3). 
In  C  the  sensory  cell  (1)  and  the  contractile  element  are  separate  cells,  but 
the  connection  between  the  two  is  maintained  by  an  interpolation  of  a  new 
nei-^'e  cell  receiving  an  afferent  extension  (3)  from  the  sensory  cells  and 
giving  off  an  efferent  extension  (5)   of  the  muscle  cell. 


fibers  originates  in  the  network  just  described  and  terminates 
around  muscular  cells  (cells,  in  other  words,  which  have  acquired  in 
the  process  of  specialization  the  highest  perfection  for  that  in- 
dividual animal  of  the  vital  phenomenon  of  contraction).  Be- 
sides these  two  sets  of  nerve  fibers,  another  set  of  fibers  containing 
small  collections  of  cells  also  exists  beneath  the  margins  of  the 
umbrella. 

6 


THE  NERVOUS  SYSTEM 

The  various  sensitive  cells  on  the  surface  present  differences  in 
their  capabilities  of  responding  to  various  stimuli.  Such  differ- 
ences represent  specialization  of  the  function  of  excitability.  Some 
are  more  sensitive  to  light,  others  to  the  weight  of  a  crystal  of  lime 
developed  near  them,  and  still  others  to  chemical  and  contact  stim- 


-TtliTACLE-S 


Fig.  2. — Diagram  of  a  jelly  fish. 
In  this  organism  the  central  nervous  cells  are  peripherally  placed. 


uli.  By  cutting  off  the  marginal  ring  with  its  marginal  bodies  we 
will  remove  the  special  sense  organs  and  the  ganglion  cells  of  the 
umbrella.  Such  a  mutilated  jelly  fish  lies  perfectly  motionless  in 
the  water.  It  is  incapable  of  any  automatic  activity  because  de- 
prived of  cells  sensitive  to  external  changes  its  muscle  cells  receive 
no  stimuli.    If  a  stimulus  is  applied  to  the  cut  nerves  running  to 

8 


THE  NERVOUS  SYSTEM 


the  contractile  cells  within,  the  jelly  fish  will  contract.     Under 

these  conditions  the  manubrium  will  bend  in  the  direction  of  the 

stimulus. 

A  more  Advanced  Stage  with  Centrally  placed  Ganglion  Cells 

—  In  the  jelly  fish  the  ganglion  cells,  which  we  may  term  perhaps 

switch  stations  or  relay  stations,  are  sit- 
uated around  the  periphery  of  the  body. 
It  will  be  a  manifest  advantage  to  an 
animal  to  have  these  switch  stations  sit- 
uated centrally.  Animals  with  cen- 
trally situated  stations,  such  as  the 
worms,  represent  the  next  stage  in  the  de- 
velopment of  a  nervous  system.  (Fig.  4.) 
The  .  Crayfish  —  A  still  further  ad- 
vance is  represented  in  animals  such  as 
the  crayfish,  in  which  the  head  ganglia, 
those  in  the  direction  in  which  the  ani- 
mal moves  forward,  show  a  special  de- 
velopment. 

In  these  animals  we  have  the  rudi- 
ments of  projicient  sense  organs,  organs 
furnishing  the  animal  with  information 
of  what  is  in  the  course  of  its  advance. 
They  may  be  not  improperly  termed  or- 
gans of  foresight.  Through  the  con- 
necting strands  of  fibers  between  these 
anterior  organs  and  the  ganglia  behind 
them  impulses  may  be  sent  to  check  for- 
ward movement  when  danger  ahead  is 
scented.  These  impulses  are  the  begin- 
nings of  inhibitory  impulses.  In  all 
these  primitive  forms  of  nervous  sys- 
tems, as  in  the  jelly  fish,  the  nervous 

system  starts  its  development  from  the  surface  epithelial  cells. 
The  Sensory  Cell  —  The  differentiated  peripheral  sensory  cell 

possesses  two  processes  —  a  short  one  passing  to  the  surface,  and  a 

long  one  passing  back  to  intermingle  with  a  network  of  fibers  in  the 

interior  of  the  animal.     (Fig.  5.) 

The  Central  Ganglion  —  This  network  also  contains  ganglion 

10 


Fig.  3.— Illustrating  the  com- 
munications between  the 
muscle  (1)  on  one  side  of 
the  umbrella  and  the  sen- 
sory epithelium  (2)  upon 
the  other  side  through  the 
peripherally  placed  cells 
(3). 


THE  NERVOUS  SYSTEM 


Fig.  4. — Illustrating  the  stages  in  the  evolution  of  a  centrally  placed  nerve  cell. 

In  1  direct  communication  between  the  muscle  and  sensory  cell. 

In  2  indirect  communication  between  the  sensory  cell  and  the  muscle 
through  a  peripherally  placed  nerve  cell. 

In  3  indirect  communication  between  the  sensory  cell  and  the  muscle 
through  a  centrally  placed  nerve  cell. 

cells,  the  processes  of  which  also  intermingle  with  terminal  divisions 
of  the  processes  of  the  differentiated  surface  epithelial  cells.  The 
intermingling  of  the  fibers  forms  a  network  embedded  in  a  granular 
substance  more  or  less  encapsulated  and  forming  a  ganglion. 
"While  many  of  the  fibers  of  the  ganglion  cells  participate  in  the 


Lumbriciis 


Verfehrafa 


Fig.  5. — Diagrams  showing  the  relative  position  of  the  sensory  cell  in  lum- 
bricus,  nereis,  and  vertebrata.     (Quain.) 

12 


THE  NERVOUS  SYSTEM 

formation  of  th§  network,  one  long  process  from  some  of  the  gan- 
glion cells  passes  to  a  muscle  cell  of  the  animal.  It  is  believed  that 
some  divisions  of  the  long  fibers  from  the  differentiated  sensitive 
epithelial  cell  may  become  a  part  of  the  central  ganglion  cell  and 
pass  directly  through  it.  If  this  occurs  it  is  exceptional,  but  it  is 
significant  that  some  fibers  of  the  terminal  network  from  the  differ- 
entiated sensitive  epithelial  cell  may  pass  directly  into  a  fiber  run- 
ning to  a  muscle  without  at  any  time  becoming  a  part  of  a  central 


Fig.   6. — Transverse   section  of  a  human  embryo   of  24  mm.      (Quain.) 
ent,  entoderm  of  yolk-sac;  the  lines  indicate  the  points  of  the  splanchno- 
pleuric  layers  which  will  come  together  to  cut  off  the  gut  from  the  cavity  of 
the  yolk-sac;  my,  outer  wall  of  mesodermic  segment;  mc,  the  part  of  its  wall 
•which  forms  the  muscle-plate;  sc,  sclerotome;  coe,  ccelom. 


nerve  cell.  This  primitive  system  is  thus  composed  of  two  ele- 
ments —  the  receiving  element,  which  is  the  differentiated  sensitive 
epithelial  cell  with  its  short  and  long  process,  and  the  reactive  ele- 
ment, or  the  peripherally  running  nerve  to  the  muscle,  which  may 
or  may  not  arise  in  a  central  nerve  cell.  The  one  is  called  the  sen- 
sory or  afferent  neuron  and  the  other  the  motor  or  efferent  neuron. 

The  Embryological  Development  of  the  Nervous  System  of  the 
Vertebrates  —  The  nervous  system  of  vertebrates  is  developed  from 
the  epithelium  of  a  groove  which  forms  upon  the  dorsum  of  the 
embryo.  This  groove  subsequently  becomes  transformed  into  a 
canal.  At  the  front  end  three  cavities  become  formed  from  which 
the  three  brains  develop.  From  the  greater  length  of  the  canal 
posteriorly  the  spinal  cord  forms.     (Figs.  6-9.) 

The  Spongioblasts  and  Neuroblasts  —  The  canal  is  formed  of 

14 


THE  NERVOUS  SYSTEM 

columnar  cells  between  the  outer  ends  of  which  small  rounded  cells 
are  found.  From  the  columnar  cells,  called  spongioblasts,  is  formed 
the  neuroglia  by  the  production  of  branching  processes.  Many  of 
the  columnar  cells  wander  externally  and  become  transformed  into 
round  cells  with  many  branches.  These  branches  form  the  sup- 
porting network  of  the  nervous  system,  the  neuroglia.     (Figs.  10- 


J.- 


Amnion. 

/ 
/ 

Neural     groove.   - 

'\ 

r 

Neurenteric  canal.  "  — 

Primitive  streali.  — 
Abdominal  stalk.  T." 


1 


./ 


\ 


Fig.  7. — Surface  view  of  early  human  embryo,  2  mm.  in  length  (after  Graf.  v. 
Spec.)    X   30   diameters.      (Quain.) 
The    amnion    is   opened,   and    on  the   blastoderm   are   seen   the    primitive 
streak,  the  dorsal  opening  of  the  neurenteric  canal,  and  the  neural  groove. 

13.)     The  round  cells  appearing  in  the  intervals  between  the  outer 
ends  of  the  columnar  cells  are  termed  neuroblasts. 

The  Development  of  the  Sensory  and  Motor  Nerve  Fibers  — 
From  the  neuroblasts  grow  out  a  process  Avhich  at  first  has  a  bulb- 
shaped  extremity.  (Fig.  15.)  By  continued  growth  of  the  process 
finally  reaches  the  periphery,  to  end  in  a  muscle  or  gland.  (Figs. 
14,  15.)  This  process  is  called  the  axis  cylinder  of  the  nerve  cell 
After  the  growth  of  the  axis  cylinder  is  well  advanced  other  proc- 
esses grow  out  from  the  cell  and  terminate  ultimately  vx  3;  series,  of 

16 


THE  NERVOUS  SYSTEM 

branches  called  dendrites.  These  cells  constitute  the  efferent  path 
of  the  central  nervous  system.  The  afferent  path  develops  from 
cells  formed  outside  the  primitive  neural  groove  from  cells  which 


n.  f.    n.  gr.     n.  f. 


Fig.  8. — Transverse  sections  of  the  human  embryo  of  2  mm.  represented  in 

Fig.  7.  (Quain.) 
In  I,  which  is  most  anterior,  the  fore-gut  is  separated  off  from  the  yolk-sac. 
n.gr.,  neural  groove;  n.j.,  neural  folds;  n.pl.  (in  III),  neural  plate;  mes}, 
intra-embryonic  mesoderm;  p.,  pericardial  coelom;  am.ect.,  amniotic  ecto- 
derm; mes.",  amniotic  mesoderm;  tnt.,  entoderm-  of  yolk-sac;  mes?,  meso- 
derm of  yolk-sac;  not. -pi.  (in  III),  notochord-plate. 


form  a  longitudinal  thickening  just  external  to  the  latter.  Prom 
these  cells  two  processes  grow  out,  one  from  each  pole.  (Figs.  17- 
20.)  The  peripheral  one  grows  to  the  surface  to  terminate  in  a 
sentient  epithelial  cell.    The  central  one  grows  internally  into  the 

18 


THE  NERVOUS  SYSTEM 


5^^r 


VSj 


t 


Fig.  9. — Closure  of  neural  canal  of  human  embryo,  showing  the  cells  of  the 
neural  crest  becoming  separated  to  form  the  germs 
of  the  spinal  ganglia.     (Quain.) 
A,  canal  still  open;  B,  canal  closed. 


Fig.  10. — Neuroglia  cells  and  fibres  from  the  white  matter  of  the  human 
cerebellum  stained  by  Weigert's  neuroglia  stain.  A,  Neuroglia  cell;  B, 
blood-vessel  cut  longitudinal^^  and  C,  blood-vessel  cut  transversely,  show- 
ing enveloping  neuroglia  fibres;  a,  neuroglia  fibres;  h,  cytoplasm  of  neu- 
roglia cell.     (Bailey.) 

20 


THE  NERVOUS  SYSTEM 
A  B 


Fig.    11. — A,    Neuroglia    cell — spider   type — human   cerebrum.     B,    Neuroglia 
cell — mossy  type— human  cerebrum.     (Bailey.) 


Fig.  12. — Neuroglia-cells  of  cerebellum.     Golgi   method.     (Quain.) 
a,  spider-cells;    h,  arborescent  cells;   c,  ependyma-like  cells. 

22 


THE  NERVOUS  SYSTEM 


Fig.  13. — A  neuroglia-cell,  isolated  in  33  per  cent,  alcohol.     (Quain  ) 


Fig.  14. — A,  ventral  root-fibres;  B,  dorsal  root-fibres;  C,  a  neuroblast  be- 
ginning to  bud  out;  D,  a  neuroblast  with  long  fibre  passing  towards  ven- 
tral commissure;  E,  a  motor  neuroblast  with  a.xon  and  dendrons;  F,  a 
motor  neuroblast  with  axon  only:  the  axon  is  expanded  at  the  growing 
end;  a,  a,  neuroblasts  with  axons  growing  into  the  lateral  column;  c,  grow- 
ing end  of  axon  of  a  commissural  fibre;  d,  a  cell  of  the  spinal  ganglion. 
(Quain.) 


24 


THE  NERVOUS  SYSTEM 


Fig.   15. — Neuroblasts   from   the   spinal   cord   of   a   third-day   chick-embryo. 

(Quain.) 
A,  three  neuroblasts,  stained  by  Cajal's  reduced-silver  method,  showing  a 
network  of  neurofibrils  in  the  cell-body;  a,  a  bipolar  cell.     B,  a  neuroblast 
stained  by  the  method  of  Golgi  showing  the  incremental  cone   (c). 


1^1^>-'^U,-. 


Fig.  16. — Section  of  wall  of  neural  tube   (first  cerebral  vesicle)    of  chick  of 
three  and  a  half  days.     (Quain.) 
A,  germinal  layer  containing  rounded  neuroblasts,  a,   b,  c   (these  already 
possess   fibrils);   B,  bipolar  neuroblasts;    c,   enlarged  growing  end   of  axon; 
e,  an  axon  growing  tangentially. 


26 


THE  NERVOUS  SYSTEM 


Fig.  17-A. — Chick-embr3^o  of  the  fifth  day.     (Quain.) 
A,  ventral   root; '5,    dorsal    root;    C,   motor   nerve-cells;    D,   sympathetic 
ganglion-cells;  E,  spinal  ganglion-cells  still  bipolar;  F,  mixed  nerve;  b,  c,  d, 
motor  nerve-fibres  passing  to  and  ramifying  in  /,  developing  dorsal  muscles; 
e,  a  sensory  nerve-trunk. 


Fig.  17-B. — Spinal  ganglion-cells  showing  transition  from  bipolar  to  unipolar 

condition.     (Quain.) 


28 


THE  NERVOUS  SYSTEM 

spinal  cord  to  terminate  in  the  neighborhood  of  some  central  cell 
developed  from  the  original  neural  groove.  The  two  processes  of 
the  afferent  cell  at  their  origin  from  the  cell  ultimately  approach 


Fig.  18. — Diagram  of  the  arrange- 
ment of  the  sensory  nerve-fibres 
in  the  olfactory  organ  and  bulb. 
(Qiiain.) 

n,  nerve-fibre  coming  off  from 
sensor}^  nerve  cell;  gl.,  synapse 
within  olfactory  glomerulus;  .  n, 
nerve-cell  and  nerve  of  olfactory 
bulb   of  brain. 


Fig.  19. — Diagram  of  the  connec- 
tions of  the  retinal  elements. 
(Quain.) 

s,  sensory  nerve-cells;  gr.i,  iur 
ner  granules ;  m.  i.,  inner  molec- 
ular layer;  g.,  ganglion-cell;  n, 
its  nerve-fibre  process  ramifying 
m  the  nerve-centre. 


each  other  so  that  they  finally  form  a  T  and  appear  to  be  given  off 
from  a  common  stem.  Because  of  the  double  process  originally 
possessed  by  these  cells  they  are  called  in  the  early  period  of  their 
development  bipolar  cells.  (Figs.  17,  A  and  B.)  In  mammals  all 
ultimately  become  unipolar  except  the  cells  of  the  spiral  and  ves- 
tibular ganglia,  from  which  the  fibers  of  the  eighth  cranial  nerve 
grow.     These  retain  the  primitive  bipolar  arrangement. 


30 


THE  NERVOUS  SYSTEM 

The  Development  of  the  Medullary  Sheath  —  Some  time  after 
the  outgrowth  of  the  axis  cylinder  the  medullary  sheath  is  formed, 
apparently  through  the  agency  of  the  axon  itself.    Th«  philogenet- 


auditory 


gustatory 


tactile 


Fig.  20. — Diagram  showing  the  mode  of  termination  of  sensory  nerve-fibres 
in  the  auditory,  gustatory,  and  tactile  structures  of  Vertebrata.     (Quain.) 

ically  youngest  fibers  in  the  body  acquire  a  medullary  sheath  later 
than  others.  Representatives  of  this  class  are  the  fibers  of  the 
pyramidal  tracts  and  the  long  posterior  columns  of  the  spinal  cord. 


32 


THE  NERVOUS  SYSTEM 

THE   MORPHOLOGY   OP   NERVOUS    TISSUE 

The  Structure  of  a  Nerve  Cell  (Figs.  21-30)  —  A  nerve  cell 
possesses,  like  all  cells,  a  nucleus.  The  nucleus,  though  of  large 
size,  contains  very  little  chromatin,  generally  collected  as  two  small 
nucleoli  within  the  nucleus.  Throughout  the  nerve  cell  run  many 
fibrillse  which  appear  in  well  prepared  specimens  as  delicate  stria- 
tions.  These  fibrillae  are  continued  out  of  the  cell  into  the  processes 
of  the  cells  between  the  Nissl  substance.  The 
Nissl  substance  is  very  abundant  except  at  that 
region  from  which  the  axis  cylinder  leaves  the 
cell.  In  this  region  many  fibrillse  are  collected 
together  to  enter  the  axis  cylinder.  It  is  called 
the  axon  hillock  of  the  cell.  The  cell  processes 
are  of  two  kinds  and  have  already  been  indi- 
cated. 

The    Axis   Cylinder    and   Dendrites  —  The 
axis  cylinder  is  smaller  than  the  other  processes, 
where  it  leaves  the  cell,  but  much,  longer,  run- 
Fig.  21.— Two  mo-  ning,  in  the  case  of  motor  cells  of  the  spinal 
tor     nerve -cells  -,..■,  •    ^  r?  ,  i      i     ■, 

from    the    dog.  cord,  to  the  periphery  oi  the  body. 

(Quam.)  The  dendrites  are  usually  thick  where  they 

after  a °perfod   of   ^^^^®   ^^®    ^^^^   ^^^^   ®^^^   break   up    into  many 

prolonged      activ-  processes  which   form  a  network  with  similar 

from^^prep£ations  P^^ocesses  of  other  cells  not  far  from  the  cell 

by     Dr.     Gustav  from  which  they  originate. 

^^^^■^  Neurons  —  A  nerve  cell  with  its  processes  is 

termed  a  neuron.    The  function  of  neurons  is  to 

transmit  nervous  impulses  and,  corresponding  to  the  direction  of 

the  impulse,  there  are  two  varieties  of  neurons  —  the  sensory  or 

afferent  neurons,  and  the  motor  or  efferent  neurons. 

An  afferent  neuron  functionally  connected  through  the  central 
nervous  system  with  an  efferent  neuron  constitutes  a  reflex  arc. 
Though  an  impulse  may  be  transmitted  in  either  direction  along  a 
nerve  fiber  it  can  only  traverse  a  reflex  arc  in  one  direction.  This 
phenomenon  is  termed  the  law  of  forward  direction. 

The  Structure  of  Nerves  (Figs.  31-32)  —All  the  nerves  which 
are  given  off  from  the  central  nervous  system,  the  brain  and  spinal 
cord,  possess  a  medullary  sheath.  This  consists  of  a  fatty  substance 
termed  myelin,  imbedded  between  the  meshes  of  a  network.     The 

34 


THE  NERVOUS  SYSTEM 


Fig.     22-A. — Ramified     nerve-cell 
from  ventral  horn  of  spinal 
cord  of  man.     (Quain.) 
a,  axis-cylinder  process;  b,  cell- 
body  with  nucleus  and  clump  of 
pigment-granules;  d,  d,  dendrons. 


Fig.  22-B. — Axis-cylinder  process 
of  a  nerve  cell.  (Quain.) 
X,  X,  portion  of  nerve-cell  from 
spinal  cord  of  ox,  with  axis-cylin- 
der process,  a,  coming  off  from  it 
and  acquiring  at  a^  a  medullary 
sheath,   highly  magnified. 


36 


THE  NERVOUS  SYSTEM 


Fig.  23. — Multipolar  and  unipolar  types  of  nerve-cell.     (Quain.) 

A,  large  pyramidal  cell  of  cerebral  cortex,  human,  Nissl  method.  (Cajal.) 
a,  axon;  b,  cell-body;  c,  apical  dendron;  d,  placed  between  two  of  the  basal 
dendrons,  points  to  the  nucleus  of  a  neuroglia-cell. 

B,  unipolar  cell  from  spinal  ganglion  of  rabbit,  Nissl  method.  (Cajal.) 
a,  axon;  h,  circumnuclear  zone,  poor  in  granules;  c,  capsule;  d,  network 
within  nucleus;  e,  nucleolus. 


38 


THE  NERVOUS  SYSTEM 


Fig.   24. — Nerve-cells    of   kitten    (from   the    anterior    corpora    quadrigemina) 
showing  neuro-fibrils. 
a,  axon;  b,  c,  d,  various  parts  of  the  intracellular  plexus  of  fibrils. 


40 


THE  NERVOUS  SYSTEM 


Fig.  25. — Nerve-cells  of  lizard:   A   and  D   during  activity,   B   and  C  during 
hibernation.     (Quain.) 
o  (in  5),  axon;  b,  h  (in  A  and  B),  knob-like  endings  of  extraneous  fibrils; 
c,  d  (in  C),  superficial  and  deep  fibril  networks. 


42 


THE  NERVOUS  SYSTEM 


Fig.  26. — A  long-axoned   nerve-cell   from  the  cerebral   cortex.     (Quain.) 
a,  axis-cylinder  process  with  collaterals;  d,  d,  dendrons;   h,  body  of  cell. 


44 


THE  NERVOUS  SYSTEM 


Fig.  27. — A  short-axoned  cell  from  the  cerebral  cortex.  Golgi  method.   (Quain.) 
a,  a! ,  a",  axon  and  its  ramification;  d,  d,  d,  dendrons. 


46 


THE  NERVOUS  SYSTEM 


Fig.  28. — Cell  from  cerebral  cortex,  showing  varicosities  on  its  dendrons  and 
not  spines.     Methylene-blue  method.      (Quain.) 
a,  axon;  h,  c,  a  branching  collateral  (both  this  and  the  main  axon  show  a 
medullary  sheath) ;  d,  varicose  dendrons, 


48 


THE  NERVOUS  SYSTEM 


Fig.    29. — Synaptic   ramificauons   of   axon   of   one   nerve-cell,   B,   around   the 

bodies  of  other  cells,  A.    From  the  cerebellum  of  the  rat.     (Quain.) 

a,  b,  c,  ramifying  axon;  d,  dendrons. 


Fig.  30. — Two  motor  cells  from  the  rabbit's  spinal  cord,  which  show  chromat- 

olysis  as  the  result  of  section  (fifteen  days  previously)  of  the 

nei've-fibres  which  arise  from  them.     (Quain.) 

In  A  the  chromatolysis  is  rather  less  advanced  than  in  B.     In  both  the 

nucleus  has   moved  to  the  periphery,   and   the   cell-substance    (6   and   c)    is 

swollen,     a,  axon-process  of  A. 


Fig.  31. — Transverse-  and  longitudinal   section   of   medullated   nerve-fibre    of 
frog   (osmic  acid  and  acid  fuchsine).      (Quain.) 
The  longitudinal  section  shows  one  node  of  Ranvier  and  two  of  Lanter- 
mann's  clefts.     The  fibrillar  structure  of  the  axis-cylinder  is  shown  in  both 
longitudinal  and  transverse  section. 

50 


THE  NERVOUS  SYSTEM 


network  is  composed 
B 


of  a  substance  termed  neurokeratin.  Outside 
the  myelin  substance  is  a  sheath 
termed  the  neurolemma.  Inside  the 
myelin  and  separating  it  from  the  axis 

—  ax  cylinder  is  the  axolemma.  The  axis 
cylinder  itself  is  composed  of  many 
fine  fibrillae,  the  so-called  neurofibrillaB. 
At  certain  intervals  along  the  nerve 
fiber,  intervals  proportionate  to  the 
diameter  of  the  nerve  fiber  and  vary- 
ing from  80  to  600  microns,  the  mye- 
lin substance  suffers  interruption  so 
that  the  medullary  sheath  dips  down 
to  touch  the  axis  cylinder.  These  in- 
terruptions are  called  the  nodes  of 
Banvier.  The  nerve  fibers  of  the 
peripheral  nerves  run  in  bundles,  sur- 
rounded and  held  together  by  a  con- 
nective tissue  sheath  termed  the  peri- 
neurium. 


Fig.  32. — Scheme  of  structure  of  medullated 

peripheral  nerve  fibre  of  a  fish. 

(Nemileff.) 

A,  Cross  section;  B,  longitudinal  section; 
on  left  fibre  is  shown  as  stained  intra  vitam 
with  methylene  blue ;  on  right,  myelin  is 
shown  black  as  in  osmic  acid  staining  with 
the  incisures  of  Schmidt  indicated;  sz,  cells 
of  sheath  of  Schwann;  n,  their •  nuclei ;  ss, 
j^';  sheath  of  Schwann;  sp,  processes  of  the 
cells  of  sheath  of  Schwann  or  the  myelin 
sheath  network;  le,  larger  trabeculae  of  pro- 
toplasmic framework  of  medullary  sheath 
arranged  obliquely  to  axis-cylinder  and 
forming  the  so-called  "funnels";  leo,,  clear 
streaks  in  fibres  treated  with  osmic  acid,  cor- 
responding to  le^  incisures  of  Schmidt;  7no, 
myelin  blackened  with  osmic  acid^a.-K  axis- 
cylinder;  pa,  periaxial  space  around  axis- 
cylinder;  f/,s-,  "coagulated  fluid"  in  periaxial 
space;  pf,  peripheral,  non-fibrillar  part  of 
axis-cylindej))^/,  neurofibrils  of  axis-cylinder; 
r,  ring-like  thickening  of  Schwann's  sheath 
at  node  of  Ranvier;  o,  cavity  in  r.    (Bailey.) 


52 


THE  NERVOUS  SYSTEM 

The  Varieties  of  Peripheral  Endings  of  Sensory  Nerves  —  The 
peripheral  process  of  the  afferent  nerve  cell  forms  a  connection 
with  the  peripheral  epithelium  in  a  variety  of  ways. 


Fig.   33. — Nerve   and  nerve   endings  in   the  skin   and  hair  follicles.      (After 

G.  Retzius.) 
As,  Outer  root  sheath;  c,  most  superficial  nerve-fibre  plexus  in  the  cutis; 
dr,  sebaceous  glands;  h,  the  hair  itself;  hst,  stratum  corneum;  is,  inner  root 
sheath  of  hair;    n,   cutaneous  nerve;   rm,  stratum  germinativum    Malpighii. 
(Bailey.) 


1.  In  some  instances  it  merely  terminates  by  ramifying  between 
epithelial  cells.     Losing  its  medullary  sheath  it  divides  a  number 

54 


THE  NERVOUS  SYSTEM 


>^ 


of  times.    Each  division  ending  in  a  little  knob  between  epitbelial 


cells. 


(1) 
(2) 
(3) 
(4) 
(5) 
(6) 
(7) 


Fig.  33.)     Nerve  fibers  end  in  this  manner  which  run: 

To  the  skin. 

To  the  mucous  membranes. 

To  connective  tissue. 

To  the  glandular  epithelium. 

To  certain  serous  surfaces. 

To  the  outer  sheath  of  the  root  of  a  hair  follicle. 

To  the  teeth.    Whether  the  dentine  is  penetrated  by  nerve 
fibers  is  a  matter  of  dispute. 

2.  In  certain  regions  of  the  body  where  special  sensitiveness  is 
required  these  endings  are  formed  by  a 
combination  of  complicated  variations 
of  the  sensory  epithelium  with  the 
nerve  ending.  The  simplest  of  these 
special  end  organs  is  the  tactile  cell.  It 
consists  of  an  epithelial  cell  with  a  pro- 
longed inner  extremity  which  comes 
into  contact  with  a  leaf-like  expansion 
of  the  end  of  the  nerve  fiber. 

3.  A  more  complex  ending  is  the 
compound  tactile  cell.  This  consists  of 
several  epithelial  cells  grouped  together 
and  in  contact  with  one  nerve  ending. 
Representatives  of  this  class  are  the  cor- 
puscles of  Grandry  and  MerkeVs  cor- 
puscles,    (^igs.  34  and  36.) 

4.  End-  hulb.  In  this  form  the  bul- 
bous end  of  the  axons  terminate  in  a 
special  granular  matter  inclosed  in  a 
capsule  of  flattened  connective  tissue 
like  cells.  They  occur  in  the  mouth  and 
conjunctiva.     (Fig.  35.)         ^\J\n  - 

5.  Compound  end  bulbs  are  combinations  of  several  simple  end 
bulbs  containing  several  nerve  endings.  They  occur  in  the  nose, 
rectum,  peritoneum  tendon,  ligaments,  joints  and  in  the  trunks  of 
nerves  upon  the  glans  penis  and  clitoris.     (Fig.  37.) 

6.  Pacinian  hodies.  In  this  form  the  axis  cylinder  terminates  in 
a  rod  which  is  inclosed  in  alternate  concentric  layers  of  a  modified 

56 


Fig.  34. — Tactile  corpuscle 
within  a  papilla  of  the 
skin  of  the  hand,  stained 
with  chloride  of  gold. 
(Quain.) 

n,  two  nerve-fibres  passing 
to  the  corpuscle;  a,  a,  vari- 
cose ramifications  of  the 
axis-cylinders  within  the 
corpuscle. 


THE  NERVOUS  SYSTEM 

a  t  t 

I  A 


Fig.  35. — Herbst  corpuscle  of  duck.     (Quain.)     x  380  diameters. 
n,  medullated  nerve-fibres;  a,  its  axis-cylinder,  terminating  in  an  enlarge- 
ment at  end  of  core;   c,  nuclei  of  cells  of  core;   t,  nuclei  of  cells  of  outer 
tunics;  t',  inner  tunics. 


Fig.  36. — Corpuscles  of  Grandry  from  the  duck's  tongue.     (Quain.) 
A,  composed  of  three  cells,  with  two  interposed  discs,  into  which  the  axis- 
cylinder  of  the  nerve,  n,  is  obsei'ved  to  pass ;  in  B  there  is  but  one  tactile 
disc  enclosed  between  two  tactile  cells. 


V 


--fer^ 


Fig.  37. — A  medullated  fibre  terminating  in  several  end-bulbs  in  the  human 
peritoneum.     Lower  power.     Methylene-blue   preparation.     (Quain.) 

58 


THE  NERVOUS  SYSTEM 


Fig.    38. — Magnified    view    of    a    Pacinian    body    from    the    cat's    mesentery. 

(Quain.) 
n,  stalk  of  corpuscle  with  nerve-fibres,  enclosed  in  sheath  of  Henle,  passing 
to  the  corpuscle  n' ,  its  continuation  through  the  core,  vi,  as  axis-cylinder  only; 
a,  its  terminal  arborization;  c,  d,  sections  of  epithelioid  cells  of  tunics,  often 
mistaken  for  the  tunics  themselves;  /,  channel  through  the  tunics  which  ex- 
pands into  the  core,  of  the  corpuscle. 


60 


THE  NERVOUS  SYSTEM 


■^^-^ — ■ 


_«;__,_ 


:»Vij^? 


Fig.  39. — Nerve-endings  upon  the  intrafusal  muscle-fibres  of  a  muscle-spindle 

of  the  rabbit.     Moderately  magnified.     Methylene-blue 

preparation.     (Quain.) 

a,  large  meduUated  fibre  coming  oft"  from  "spindle"  nerve  and  passing  to 
end  in  an  annulo-spiral  termination  on  and  between  the  intrafusal  fibres; 
h,  fine  medullated  fibres  coming  off  from  the  same  stem  and  dividing.  Its 
branches,  c,  pass  towards  the  ends  of  the  muscle-fibres  and  terminate  in  a 
number  of  small  localized  arborizations,  like  end-plates. 


Fig.  40. — Sensory  nerve  terminating  in  arborizations  around  the  ends  of 
muscle-fibres.     (Quain.) 


Fig.    41- -An    annulo-spiral    ending    of    intrafusal    fibre.      Highly    magnified. 
Methylene-blue    preparation.      (Quain.) 

62 


THE  NERVOUS  SYSTEM 


Fig.  42. — Organ  of  Golgi  from  the  human  tendo  achillis.     Chloride  of  gold 
preparation.     (Quain.) 
m,   muscular  fibres;    t,  tendon-bundles;    G,   Golgi's  organ;    n,  two  nerve- 
fibres  passing  to  it. 


y> 


Fig.  43. — Ending   of  nerve-fibres  in  cardiac  muscle.     (Quain.) 


\. ..  J 

Fig.   44. — Motor   nerve-ending    in   the    abdominal    muscles    of   a    rat.     Gold 
preparation.     Magnified   170  diameters.      (Quain.) 

64 


THE  NERVOUS  SYSTEM 


Fig.   45. — Terminal   nerve-fibrils    in   an   alveolus   of   the    submaxillary    gland 

of  the  dog.     Chromate  of  silver  method.     (Quain.) 

The  extension  of  the  lumen  into  the  crescents  of  Gianuzzi  is  also  shown. 


Fig.  46. — Motor  end-organ  of  a  lizard.    Gold  preparation.     (Quain.) 
n,  nerve-fibre  dividing  as  it  approaches  the  end-organ;  r,  ramification  of 
axis-cylinder  upon,  b,  granular  bed  or  sole  of  the  end-organ;  m,  clear  sub- 
stance surrounding  the  ramifications  of  the  axis-cylinder. 


66 


THE  NERVOUS  SYSTEM 

A  B 


Fig.  47. — Nerve-ending  in  muscular  fibre  of  lizard  (lacerta  viridis).     (Quain.) 
A,  end-plate  seen  edgeways;  B,  from  the  surface;  s,  s,  sarcolemma;  pp,  ex- 
pansion of  axis-cylinder.     In  B  the  expansion  of  the  axis-cylinder  appears 
as  a  clear  network  branching  from  the  divisions  of  the  medullated  fibres. 


1 


t 
/■•■. 


„'-^^^  /^H 


b    ^^ 


y 


Fig.  48.— Ending  of  motor  nerves  m  rabbit's  muscle.    Reduced  silver  method. 

(Quain.) 
a,  axis-cylinder   of   entering   nerve;    b,   c,   parts   of   terminal   ramification 
showing  network  of  neuro-fibrils. 


68 


THE  NERVOUS  SYSTEM 

epithelium  containing  fluid  between  them.  These  occur  in  the 
palms  of  the  hands,  the  soles  of  the  feet,  in  the  parietal  peritoneum, 
the  mesentery,  mammary  gland,  tendons,  ligaments,  joints,  and 
penis,  clitoris  and  in  the  voluntary  muscles.     (Fig.  38.) 

7.  Besides  the  Pacinian  bodies  sensory  nerves  to  muscular  fibers 
terminate  in  expansions  which  form  (a)  annular,  (&)  spiral  and 
(c)  arborizing  expansions  around  the  musclar  fibers.  (Figs. 
39-41.)  -^"-^  ^ 

8.  Special  arborizations  upon  the  tendons  are  termed  organs  of 
Golgi.    (Fig.  42.) 

9.  All  motor  nerves  terminate  at  the  muscular  fibers  by  branch- 
ing in  a  mass  of  granular  substance  superficial  to  the  muscular  fiber 
but  beneath  the  sarcolemma.  This  ending  is  termed  the  motor  end 
plate.  All  these  modifications  of  endings  have  developed  for  the 
purpose  of  delicately  transmitting  slight  molecular  changes  of  a 
refined  order  to  or  from  a  sensitive  cell.     (Figs.  43-48.) 

The  more  complex  the  connection  between  the  termination  of  the 
nerve  and  the  sensitive  surface,  the  more  refined  and  delicate  and 
special  is  the  sensation  or  motor  impulse  transmitted.  In  other 
words,  in  those  regions  in  which  sensations  of  a  special  sensitive- 
ness or  of  a  special  kind  must  be  transmitted  there  is  need  of  a 
special  device,  which  exists  in  the  form  of  these  complex  nerve 
endings. 

The  importance  of  even  simple  nerve  endings  is  made  clear  by 
the  disorderly  character  of  a  reflex  excited  by  stimulating  the  cut 
nerve  endings  after  dissecting  off  the  skin. 

70 


THE  NERVOUS  SYSTEM 


PHYSIOLOGY    OF   NERVES 

The  Classification  of  Nerves  —  Nerves  may  be  classified  as  fol- 
lows : — 


Efferent . 


Excitatory 


motor 


Secretory 


'Motor 

Vasomotor 

Cardiomotor 

Visceromotor 

Pilomotor 

Salivary 

Gastric 

Pancreatic 

Sweat 


f  Motor  for  all  sub.  div.  of  motor  nerves 
Inhibitory  J 

[  Seeretoi-y  for  all  sub.  div.  of  secretory  nerves 


T'rophie 


fS 


Excitatory 


ensoiy 


Reflex 


'Visual  ,  -. 

Auditory 
Equilibrial 
Olfactory 
Gustatory 
Pressure 
Temperature 
Pain 
Hunger 
Thirst  / 

Reflex  for  various  efferent  nerves 


Inhibitoiy 


Trophic 


Inhibitory  upon  conscious  sensations  have  not 
been  demonstrated 

The  reflex  fibers  which  cause  unconscious  re- 
flexes are  known  to  be  inhibited  in  some 
cases  at  least 


72 


"h^x/rt^-^/ 


ft       I 


V7vA 


y 


uyii 


THE  NEEVOUS  SYSTEM 

The  Velocity  of  an  Impulse  along  a  Motor  Nerve  is  measured  by 
stimulation  of  tlie  nerve  of  a  muscular  nerve  preparation  at  two 
points,  separated  by  a  known  distance,  and  recording  upon  a  mov- 
ing surface  the  time  of  application  of  each  stimulus  and  the  time 
of  response  (contraction  of  the  muscle)  to  each  stimulus. 

The  difference  between  the  time  of  application  of  the  stimulus 
and  the  response  in  the  two  cases  will  be  the  time  it  has  taken  the 
impulse  to  travel  the  known  distance  which  separates  the  electrodes. 
The  velocity  in  a  frog's  nerve  is  28  meters  a  second,  and  in  warm 
blooded  animals  is  60  to  120  meters  a  second.     (Fig.  49.) 


Fig.  49. — Apparatus  arranged  for  determining  speed  of  motor  nerve  impulse. 
By  means  of  turn-over  key  (1),  the  current  from  the  cell  (2),  through  the 
inductorium  (3)  may  be  applied  to  the  nerve  at  the  two  points  (4  and  5). 
The  difference  in  time  in  the  contraction  of  the  muscle  is  indicated  by  the 
difference  in  the  rise  of  the  lever  (6)  on  the  cylinder  (7)  in  fractions  marked 
at  (8). 

The  Velocity  of  an  Impulse  along  a  Sensory  Nerve  can  only  be 
measured  by  measuring,  in  the  same  manner,  the  velocity  of  the 
electrical  change  which  accompanies  the  propagation  of  the  im- 
pulse. It  is  about  the  same  as  the  velocity  of  propagation  along  a 
motor  nerve. 

The  velocity  of  propagation  varies  with  the  species  of  animal. 
In  general  it  is  proportional  to  the  height  in  the  scale  of  life  of  the 
animal  in  question. 

The  Direction  of  the  Impulses  —  The  direction  of  propagation 
along  a  nerve  fiber  may  be  ascertained  by  noting  the  direction  of 
spread  of  the  electrical  current  accompanying  the  propagation  of 
the  impulse.  The  impulse  is  found  to  travel  in  both  directions  from 
the  point  stimulated. 

74 


THE  NERVOUS  SYSTEM 

A  Demonstration  that  Nerve  Impulses  Travel  in  both  Direc- 
tions —  The  gracilis  muscle  of  a  frog  is  separated  longitudinally 
into  halves  by  a  tendinous  intersection.  The  axis  cylinders  supply- 
ing these  two  divisions  are  divisions  of  the  axis  cylinders  them- 
selves, which  run  to  the  muscle.  Stimulation  of  the  distal  portion 
of  the  divisions  of  the  axis  cylinders  supplying  one  half  will  cause 
a  contraction  of  the  whole  muscle,  whereas  stimulation  of  the  muscle 
alone,  i.e.,  in  a  place  free  from  nerve  fibers,  will  cause  a  contraction 
in  only  one  half  of  the  muscle.  In  the  first  instance  the  impulse 
must  have  traveled  up  the  set  of  axis  cylinders  of  the  stimulated 
half  and  down  the  branches  into  the  unstimulated  half,  thus  travel- 
ing in  both  the  direction  of  the  course  of  the  nerve  in  one  part  and 
in  the  opposite  direction  to  the  course  of  the  nerve  in  the  other  part. 

Bell  and  Majendie's  Law  —  Though  an  impulse  may  travel  in 
either  direction  of  a  nerve,  the  same  nerve  cannot  be  both  afferent 
and  efferent.  This  fact  has  been  enunciated  into  a  law  by  Bell  and 
Majendie  and  is  known  as  their  law.  The  difference  in  the  function 
of  nerves  expressed  by  the  law  of  Bell  and  Majendie  is  not  depen- 
dent upon  any  essential  difference  in  the  nerve  but  solely  upon 
their  central  and  peripheral  connections,  a  fact  which  may  be  dem- 
onstrated by  grafting  experiments. 

Events  Accompanying  the  Passage  of  a  Nerve  Impulse  —  The 
Expenditure  of  Energy  —  The  fact  that  a  nerve  loses  its  irritability 
in  the  absence  of  oxygen  indicates  that  the  process  of  excitation  is 
accompanied  by  the  consumption  of  oxygen  and,  therefore,  the 
dissipation  of  energy.  The  consumption  of  energy,  however,  must 
be  extremely  small  inasmuch  as  the  most  sensitive  methods  for 
measuring  heat  have  failed  to  detect  any  rise  of  temperature  accom- 
panying the  passage  of  a  nervous  impulse. 

The  Demarcation  Current  —  If  the  terminals  of  a  delicate  gal- 
vanometer are  connected  to  a  resting  uninjured  nerve  no  current 
through  the  nerve  will  be  detected.  If,  however,  the  nerve  is  di- 
vided and  one  of  the  poles  of  the  galvanometer  circuit  is  connected 
with  the  injured  end,  while  the  other  pole  is  in  contact  with  the  side 
of  the  nerve  at  some  distant  point,  the  needle  of  the  galvanometer 
will  swing,  indicating  in  the  first  place  the  existence  of  a  current 
in  the  nerve  and  in  the  second  place  that  the  current  passes  through 
the  nerve  from  the  end  pole  to  the  lateral  pole.  In  terms  of  the 
outside  circuit  the  pole  on  the  end  of  the  nerve  is  negative  to  all 

76 


THE  NEEVOUS  SYSTEM 

other  points.  This  current  is  called  a  demarcation  current  and  is 
excited  by  the  injury  to  the  nerve  incidental  to  its  division. 

Current  of  Action  —  If  now  an  impulse  is  excited  in  the  nerve 
by  stimulating  it  above  the  site  of  application  of  the  poles  of  the 
galvanometer  the  needle  of  the  galvanometer  will  swing  in  an  oppo- 
site direction,  indicating  a  current  in  the  opposite  direction.  This 
current  is  the  current  of  action  or  the  current  accompanying  the 
passage  of  an  impulse  which  passes  from  the  stimulated  point  in 
both  directions  and  consequently  toward  the  injured  end.  It  has 
been  called  the  negative  phase  of  the  demarcation  current.  The 
demarcation  current  is  strongest  immediately  after  division  of  the 
nerve  and  quickly  subsides  as  the  nerve  dies  up  to  the  node  of 
Ranvier  nearest  to  the  cut  end.  It  may  again  be  excited  by  a  fresh 
division  above  this  node.  The  current  of  action  travels  with  the 
same  rate  as  the  nervous  impulse  —  28-33  meters  a  second.  It  is 
18  m.  in  length  and  lasts  only  6/10,000-8/10,000  of  a  second  at  any 
one  point. 

Conditions  Affecting  the  Passage  of  a  Nervous  Impulse  — 
Temperature  —  Conduction  along  a  nerve  is  much  diminished  by 
decreasing  the  temperature.  A  temperature  between  0°  and  5°  C. 
is  sufficient  to  check  conductivity  in  a  mammalian  nerve.  The 
temperature  coefficient  for  each  difference  in  temperature  of  10°  C, 
is  1.79.  This  amount  is  a  constant  factor  by  which  the  velocity 
of  conduction  along  a  nerve  fiber  may  be  multiplied  to  give  the 
velocity  at  10°  C.  higher  temperature. 

Fatigue  —  Nerve  fibers  cannot  be  fatigued,  at  least  by  excessive 
excitation,  but  a  nerve  muscular  preparation  quickly  shows  signs 
of  fatigue  from  repeated  excitation. 

Demonstration  of  the  Site  of  Fatigue  in  the  Nerve  Muscle 
Mechanism  —  After  the  preparation  has  been  fatigued  the  muscle 
may  be  excited  to  contraction  by  direct  stimulation,  showing  that 
the  muscle,  at  least,  is  not  the  most  quickly  fatigued  of  the  various 
components  of  a  muscle  nerve  preparation.  In  considering  the  seat 
of  fatigue  of  a  nerve  muscular  preparation,  besides  the  muscle, 
the  motor  end  plate  and  the  nerve  are  to  be  considered.  Two 
agents  will  enable  us  to  eliminate  the  nerve  as  the  seat  of  fatigue. 
One  is  curare  and  the  second  is  the  passage  of  the  constant  cur- 
rent. Curare  specifically  paralyzes  the  motor  end  plate.  If  it  is 
applied  to  a  muscular  nerve  preparation  the  nerve  may  be  con- 

78 


THE  NERVOUS  SYSTEM 


W,   We 


tinuously  stimulated  without  affecting  the  motor  end  plate  or  the 
muscle,  because  of  the  block  produced  at  the  motor  end  plate  by 
curare.  After  the  effect  of  the  curare  wears  off  or  after  it  is  set 
aside  by  its  antagonist  physostigmin,  the 
muscle  again  may  be  stimulated  by  stimula- 
tion of  the  nerve,  showing  that,  although  the 
nerve  had  been  excited  for  a  much  longer 
HTv^  V,.,^  time    than    would    have    been    necessary    to 

^^}  fatigue  both  the  motor  end  plate  and  the 
muscle  during  the  time  that  both  were  pro- 
tected by  the  curare,  the  nerve  is  still  capable 
of  transmitting  an  impulse. 

A  constant  current  possesses  the  power  of 
blocking  impulses  through  a  nerve.  It  may  be 
used  in  the  same  manner  as  curare  to  protect 
the  motor  end  plate  and  muscle  from  excita- 
tion during  a  period  of  prolonged  stimulation 
of  the  nerve  of  a  nerve  muscle  preparation 
above  the  point  of  application  of  the  constant 
current.     (Fig.  50.) 

Drugs  —  The  action  of  drugs  upon  nerves 
may  be  tested  by  inclosing  the  nerve  of  a 
muscle  nerve  preparation  within  a  closed 
tube.  The  nerve  issues  through  the  ends  of 
the  tube,  which  are  closed  with  normal  saline 
clay.  Into  the  tube  may  then  be  conducted 
the  vapor  of  the  drug,  the  action  of  which  it 
is  desired  to  test.  The  effect  of  these  drugs 
may  then  be  tested  upon  both  the  excitability 
of  the  nerve  and  its  conductivity. 

Excitability  may  be  tested  by.  means  of 
electrodes  which  make  connections  with  the 
portion  of  the  nerve  inclosed  within  the  tube. 
Conductivity  may  be  tested  by  electrodes 
making  contact  with  a  portion  of  the  nerve 
outside  of  that  end  of  the  tube  which  is  opposite  to  the  end  nearest 
the  muscle  end  of  the  nerve  muscle  preparation. 


Ml         Ma 

Fig.  50.  —  Indefatig- 
ableness  of  the 
nerves. 
Two  muscles,  Mi, 
M2,  furnished  with 
their  nerves,  A^'i,  N2, 
are  simultaneously 
stimulated  at  x  by  an 
induced  current.  The 
nerve,  N2,  is  anelec- 
trotonized  at  B  by  a 
constant  current,  Z, 
so  as  to  prevent  the 
impulse  reaching  the 
muscle,  M2,  thus  to 
prevent  this  muscle 
being  fatigued.  The 
muscle.  Ml,  is  quick- 
ly fatigued  and  ceases 
to  contract.  If  then 
the  cell  current  is 
broken,  while  the 
stimulation  of  the 
two  nerves  continues 
at  X,  the  muscle,  M2, 
will  be  seen  to  con- 
tract ;  therefore  its 
nerve  has  not  felt  the 
effects   of  fatigue. 


80 


THE  NERVOUS  SYSTEM 


Fig.  51. — Apparatus  for  exposing  a  portion  of  a  nerve  to  gases  and  for  testing 
the  excitability  and  conductivity  of  the  exposed  portion 

1.  Exposed  portion  of  nerve. 

2.  Tube  containing  the  gas  with  inlet  and  outlet. 

3.  Electrodes  for  testing  excitability. 

4.  Electrodes  for  testing  conductivity. 


Effect  of  Carbon  Dioxide  and  Ether,  Chloroform  and  Alcohol  — 
Carbon  dioxide  and  ether  diminish  first  excitability,  and  then  con- 
ductivity. Chloroform  rapidly  diminishes  excitability  and  conduc- 
tivity and  far  more  intensely  than  ether,  so  that  recovery  may  not 
be  complete.  Alcohol  diminishes  conductivity  without  at  first 
affecting  excitability.     (Figs.  51,  52.) 


■i: 

llllilil 

III! 

iiiijil 

'  1 1 1 1 

1 

■   '  '1  ' 

i, 

|_^-r„,p._' 

tlTHER.    — 

\ 

Fig.  52. — Illustrates  the  effect  of  ether  vapor  upon  excitability  and  con- 
ductivity. Following  the  exposure  of  the  nerve  to  ether  there  is  a  disap- 
pearance of  excitability.  The  dotted  vertical  lines  illustrate  a  response  to 
the  application  of  the  current  to  the  portion  of  the  nei*ve  surrounded  with 
ether  vapor.  The  straight  vertical  lines  indicate  a  response  of  the  nerve 
to  the  stimulation  applied  to  a  point  outside  the  portion  exposed  to  the 
ether  vapor.  The  stimulus  is  therefore  alternately  applied  to  the  nerve 
inside  and  outside  of  the  tube. 

At  1  there  is  a  disappearance  of  excitability. 

At  2  there  is  a  reappearance  of  excitability. 

At  3  there  is  a  disappearance  of  excitability. 

At  4  there  is  a  disappearance  of  both  excitability  and  conductivity. 

At  5  there  is  a  reappearance  of  conductivity  and 

At  6  a  reappearance  of  excitability. 


82 


THE  NERVOUS  SYSTEM 

EVENTS  ACCOMPANYING  THE  ELECTRICAL  EXCITATION  OF  NERVES 

The  Minimal  Effective  Stimulus  is  ascertained  by  exciting  a 
^nerve  muscular .  preparation  from  the  discharge  of  a  condenser 
charged  with  decreasing  potential  until  the  minimal  stimulus  is 
found.  (Fig.  53.)  For  frogs'  nerve  it  is  1/1000  of  an  erg  (an  erg 
being  the  amount  of  energy  produced  or  work  performed  by  the 
action  of  one  dyne  through  one  centimeter.  A  dyne  gives  an  ac- 
celeration of  one  centimeter  per  second  to  one  gram). 

Summations  —  If  several  subminimal  stimuli  are  applied  suf- 
ficiently  close  together  so  that   each   successive  stimulus  affects 


Fig.  53. — Illustrating  the  apparatus  for  exciting  the  nerve  from  a  condenser 
with   a   definite   quantity   of  electricity. 
1.    Switch  for  throwing,  first,  the  rheostat,  2,  and,  second,  the  condenser,  3, 
into  the  circuit  of  the  electrodes  upon  the  nei"ve. 

the  nerve  before  the  effect  from  the  first  one  has  passed  off  the 
combined  effect  may  produce  excitation  though  each  individual 
stimulus  would  fail  to  do  so.  This  phenomenon  is  called  sum- 
mation. 

The  Refractory  Period  —  For  a  brief  time  after  the  application 
of  an  electrical  current  to  a  nerve  it  remains  unexcited.  This 
period  is  called  the  refractory  period  and  amounts  to  .002- .0006 
of  a  second  according  to  the  temperature.  The  existence  of  a 
refractory  period  is  common  to  all  forms  of  excitable  tissue,  and 
is  best  illustrated  in  heart  muscle.  After  the  application  of  a 
stimulus  to  heart  muscle,  the  change  producing  contraction  may 
be  said  to  be  progressing,  and  it  is  during  this  period  that  the 
muscle  is  refractory  to  another  stimulus  of  the  same  strength,  for 
the  simple  reason  that  it  is  already  responding  to  the  first  stimu- 

84 


THE  NERVOUS  SYSTEM 

lus.  If,  however,  a  very  strong  stimulus  is  applied  within  the  re- 
fractory period  it  may  respond,  so  that  the  refractory  period  de- 
pends on  the  strength  of  the  stimulus  used.  However,  after  such  a 
response  it  remains  irresponsive  to  normal  stimuli  for  a  longer 
time,  thus  indicating  the  causes  upon  which  the  refractory  period 
depends,  namely  a  breaking  down  of  material  available  for  re- 
sponse, the  response  depending  upon  the  katabolic  changes. 

Site  of  the  Excitation  —  "When  the  constant  current  is  made 
use  of  to  excite  a  nerve,  an  excitation  occurs  at  the  make,  and. 


Fig.  54.— Apparatus   for  determining  the  site    of   excitation   of   the   muscle, 
whether  at  the  anode  or  the  cathode,  at  either  the  make  or  the  break. 
B,  Battery;  K,  key,  by  means  of  which  the  current  is  made  or  broken; 

C,  clamp  holding  the  muscle  by  its  middle  movable  electrodes,  EE,  capable 

of  recording  the  movements  upon  the  paper,  P. 


assuming  that  the  current  is  strong  enough,  at  the  break  also;  a 
make  excitation  starts  at  the  cathode  and  a  break  excitation  starts 
at  the  anode.  Inasmuch  as  what  is  true  for  one  excitable  tissue  is 
true,  in  this  respect,  for  another,  muscle  may  be  used  to  demon- 
strate the  fact. 

<a)  It  may  be  clamped  lightly  in  its  middle  and  the  two 
electrodes  attached  to  the  two  ends,  each  electrode  being  capable 
of  a  swmg  in  towards  the  muscle.  At  the  make  contraction  the 
cathode  electrode  will  swing  in  towards  the  muscle;  ?>,t  tbe  break 
contraction  the  anode  will  do  the  same.     (Fig.  54.) 

(b)  Inasmuch  as  injury  or  death  of  the  end  of  a  muscle  will 
prevent  its  irritability,  a  muscle  injured  at  one  end  may  be  used 
to  demonstrate  the  starting  point  of  the  contraction  at  the  make 

86 


THE  NERVOUS  SYSTEM 


and  break.     At  the  make  no  contraction  will  occur  if  the  cathode 
is  attached  to  the  injured  end,  and  vice  versa. 

Electrotonus  —  It  has  been  said  that  contraction  only  occurs 
at  the  make  and  break  of  a  constant  current.  If  the  current  is 
strong  enough  the  excitability  of  the  nerve  of  a  muscular  nerve 
preparation  may  be  so  increased  that  the  muscle  may  be  thrown 
into  a  state  of  continued  contractions,  called  closing  tetanus,  all 
the  time  during  which  the  current  is  passing. 

Excitab.  increjsed 


Excitab.  diminished 


Polariring 
Current 


^ 


Fig.  55. — Determination  of  excitability  of  the  myopolar  segment  during  the 
passage  of  a  current  through  a  certain  length  of  the  nerve. 
In  the  lower  figure  the  polarizing  current  is  ascending;  excitability  is  di- 
minished in  the  myopolar  segment.    In  the  upper  figure  the  polarizing  current 
is  descending;  the  excitability  of  the  myopolar  segment  is  increased. 

An  "after  tetanus''  may  also  follow  the  break  of  a  strong 
ascending  current  which  has  been  passing  for  a  considerable  time. 
With  moderate  or  usual  currents,  however,  no  apparent  change 
occurs  during  the  time  the  constant  current  passes. 

Electrotonus  and  Method  of  Its  Detection  —  A  change  never- 
theless does  occur  during  this  period  between  the  make  and  break 
of  a  constant  current  which  is  capable  of  detection  by  stimulating 
different  portions  of  the  nerve  by  an  induced  current  acting  as  an 
analyzer.  During  the  time  that  the  constant  current  is  passing, 
the  analyzer  will  detect  a  region  near  the  cathode  of  the  constant 
current  where  the  excitability  is  increased,  and  hence  a  greater 
stimulus  or  impulse  may  be  produced  by  a  submaximal  stimulus 
than  would  result  in  the  absence  of  the  constant  current.  In  the 
same  manner  a  region  near  the  anode  can  be  demonstrated  in 
which  the  irritability  is  diminished.     (Fig.  55.) 

88 


THE  NERVOUS  SYSTEM 

Catelectrotonus   and   Anelectrotonus  —  The   increased   irrita- 
bility at  the  cathode  is  called  catelectrotonus  and  the  diminished 

excitability  at  the  anode  is  called  anelectrotonus.  Inasmuch  aa 
the  impulse  leading  to  contraction  at  the  make  begins  at  the  cathode 
it  may  be  said  that  the  excitability  is  due  to  a  rise  of  irritability 
at  the  cathode,  dependent  upon  the  sudden  development  of  cat- 
electrotonus. In  the  same  manner  the  rise  of  excitability  at  the 
anode  accompanying  the  break  is  due  to  sudden  passing  off  oi 
anelectrotonus.  The  above  is  true  for  currents  of  moderate 
strength.  "When  stronger  currents  are  used  the  indifferent  poini 
separating  the  two  regions  of  anelectrotonus  and  catelectrotonus 
from  each  other  comes  to  lie  nearer  the  cathode,  so  that  more  anu 
more  of  the  nerve  is  in  a  condition  of  anelectrotonus. 

Pfliig'er's  Law  —  In  the  case,  therefore,  of  very  strong  cur- 
rents the  whole  interelectrodal  portion  of  the  nerve  is  in  a  con- 
dition of  anelectrotonus  and  the  depression  of  irritability  at  the 
anode  at  the  make  is  so  great  that  the  nerve  is  non-conductive  at 
this  point.  Consequently  when  strong  currents  are  used  to  pro- 
duce stimulation,  and  the  current  is  an  ascending  one,  no  im- 
pulse can  reach  the  muscle  at  the  make  because  the  make  excitation 
starts  at  the  cathode,  which  is  furthest  from  the  muscle.  In 
ascending  currents  it  is  blocked  by  the  high  degree  of  anelec- 
trotonus at  the  anode.  In  the  same  manner  at  the  break  of  descend- 
ing currents,  when  strong  currents  are  used  the  excitation  started 
at  the  anode  by  the  passing  off  of  anelectrotonus  cannot  descend 
past  the  cathode  where  there  is  a  swing  back  from  high  catelec- 
trotonus to  a  very  low  degree  of  irritability.  These  variations  in 
tne  results  of  stimulating  nerves  with  varying  degrees  of  current 
have  been  formulated  into  a  law  called  Pfluger's  law,  namely, 
tfiat  the  result  of  stimulating  a  nerve  varies  with  the  strength  of 
the  current  and  is  as  follows : 


ASCBi; 

FDING 

DESCENDING 

malce 

break 

make               break 

weak 

c 

0 

e                     0 

medium 

c 

e 

C                     e 

strong 

0 

C  or  T 

C  or  T                0 

anelectrotonus  block 

(C- 
effect.) 

-  strong 

contraction. 

c  —  contraction.      T  —  tetanus.      < 

90 


THE  NERVOUS  SYSTEM 

For  these  reasons,  when  dealing  with  induced  shocks  we  are 
only  dealing  with  make  stimuli.  The  contraction  at  the  break  of 
the  primary  circuit,  which  is  evoked  by  the  make  of  the  make  and 
break  produced  in  the  secondary  circuit,  is  stronger  than  the 
contraction  produced  at  the  make  of  the  primary,  because  the  rise 
of  current  at  the  make  in  the  primary  is  a  much  slower  change 
than  the  fall  of  current  at  the  break.  In  other  words  the  intensity 
of  the  currents  induced  in  the  secondary  coils  is  proportional  to 
the  rate  of  change  of  the  current  in  the  primary  coil. 

Application  to  the  Human  Being  —  These  results  cannot  be 
aj  plied  to  human  nerves  with  the  same  exactness,  because  of  the 


Fig.  56. — ^Diagram  showing  the  internal  polarization  of  the  tissues. 
All  along  the  lines  of  the  flow  of  the  current,  going  from  one  pole  to  the 
other,  secondary  polarities  are  developed  across  the  heterogeneous  portions, 
traversed  by  electrolytic  conduction. 


impossibility  of  the  direct  application  of  the  electrodes  to  the 
human  nerves.  It  is  usual  to  apply  one  electrode  (a  stimulating 
effect  being  most  readily  obtained  when  the  stimulating  electrode 
is  the  cathode)  over  some  point  at  which  the  various  motor  nerves 
lie  nearest  to  the  surface.  The  other  electrode,  the  indifferent  one, 
is  applied  over  some  other  region  of  the  body.  Inasmuch  as  the 
current,  as  it  nears  the  cathode,  becomes  concentrated  from  a 
more  diffuse  condition  at  a  distance  from  this  electrode  called 
the  peripolar  region,  the  current  is  strongest  nearest  to  the  elec- 
trode as  it  passes  across  the  nerves.  It  exists  as  opposite  signs  on 
the  two  sides  of  the  nerve  and  is  stronger  on  the  side  nearest  the 
cathode.  (Fig.  56.)  Pure  cathode  and  anode  effects  are  not  ob- 
tainable. Applying  the  current  in  the  manner  described  to  the 
human  being  gives  the  following  phenomena  in  the  order  of  the 
strength  of  contraction  produced : 

92 


THE  NERVOUS  SYSTEM 

C  C  C  (cathode  closing,  i.e.  make  contraction) 

A  C  C  (anode  closing  contraction) 

A  0  C  (anode  opening,  i.e.  the  break  contraction) 

C  0  C  (cathode  opening  contraction) 

Polarization  and  Its  Explanation  in  the  Extrapolar  Region  of 
the  Nerve  —  The  length  of  a  nerve  between  the  electrodes  of  a 
current  applied  to  the  nerve  is  called  the  intrapolar  or  intraelec- 
trodal  portion.  By  sensitive  galvanometers  it  may  be  shown  that 
a  current  passes  also  through  the  extrapolar  region  of  the  nerve 
during  the  passage  of  a  constant  current.  This  current  is  in  the 
direction  of  the  constant  current  which  is  applied  to  the  nerve.    It 


NerTe. 


Anelectrotonic 
current. 


Polarizing 
current. 


Catelectrotonic 
current. 


Fig.  56a. — Polarization  of  the  nerve  in  its  two  extrapolar  segments  and 
production  of  electrotonic  currents  in  these  two  segments. 
The  middle  region  is  traversed  by  a  constant  current  (polarizing  current). 
The  extrapolar  regions  show  currents  of  polarization  of  the  same  direction 
as  the  preceding,  but  unequal  in  intensity.  The  anelectrotonic  current  is 
more  intense  than  the  catelectrotonic  current. 


is  a  different  current  from  the  current  of  action.  The  same  extra- 
polar  current  may  be  excited  by  the  application  of  a  constant  cur- 
rent to  an  artificial  model  of  a  nerve,  consisting  of  a  platinum  wire 
contained  within  a  tube  and  surrounded  within  the  tube  by  normal 
saline  solution  or  any  other  electrolyte.  It  will  not  occur,  how- 
ever, if  the  model  is  made  of  a  zinc  wire  immersed  in  a  satu- 
rated solution  of  zinc  sulphate.  The  phenomenon  of  these 
extrapolar  currents  is  purely  physical  and  depends  upon 
polarization  produced  in  the  extrapolar  regions  of  the  nerve.  The 
nerve  sheath  may  be  regarded  as  composed  in  part  of  a  solution 
electrolytes.     (Fig.  56c.) 

Upon  the  sheath  in  the  neighborhood  of  the  positive  pole  of 
the  polarizing  current  negative  ions  collect  and  in  the  same  manner 

94 


THE  NERVOUS  SYSTEM 

positive  ions  collect  in  the  neighborhood  of  the  negative  pole.  In 
fact  it  is  only  due  to  the  fact  that  these  two  sets  of  ions  are  at- 
tracted to  the  poles  and  give  up  their  charges  to  them  that  any 
current  from  the  cell  passes  through  the  nerve  at  all.  These 
attracted  ions  at  the  points  of  application  of  the  electrodes  create 
in  this  region  a  difference  of  potential  which  extends  to  the  extra- 
polar  region. 

The  Current  of  Positive  Polarization  and  Its  Negative  Varia- 
tion —  In  consequence  of  this  fact  a  current  will  pass  in  the  extra- 
polar  region.  This  current  is  called  the  current  of  polarization. 
(Fig.  56a.)    If  now  the  electrodes  of  the  constant  current  are  taken 


r^ 


rdh 


ui 


Fig.  56b. — Post-electrotonic  intrapolar  currents  produced  after  the  cessation  of 

the  polarizing  current. 

I,  polarizing  current;  II,  ordinary  post-current  of  contrary  direction  or  the 

current   of   negative   polarization;    III,   post-current    whose    direction   is   the 

same  as  that  of  the  polarizing  current  or  the  current  of  positive  polarization. 


away  from  the  nerve  and  in,  their  place  the  poles  of  a  galvanometer 
are  applied,  the  galvanometer  will  show  a  temporary  current  in  the 
opposite  direction  to  that  in  which  the  constant  current  was  pre- 
viously flowing,  though  immediately  preceding  this  current  in  the 
opposite  direction  there  will  be  momentary  current  in  the  same 
direction.  This  momentary  current  in  the  same  direction  is 
known  as  the  current  of  positive  polarization,  and  that  in  the 
opposite  direction  as  the  current  of  the  negative  variation  of  the 
polarizing  current.  The  current  of  positive  polarization  is  really 
the  current  of  action  excited  by  the  break  produced  when  the 
electrodes  are  lifted  off.  The  negative  variation  of  the  polarizing 
current  is  due  to  the  difference  of  potential  created  at  the  places 
where  the  poles  of  the  constant  or  polarizing  current  had  collected 
ions  of  unlike  sign  to  that  of  the  poles  of  the  polarizing  current 
in  the  region  of  the  poles.  Inasmuch  as  the  ions  thus  collected 
at  these  spots  are  of  unlike  sign  to  that  of  the  poles,  the  current 
will  flow  in  the  opposite  direction  to  that  of  the  polarizing  cur- 

96 


THE  NERVOUS  SYSTEM 

rent.     (Figs.  56b  and  56c.)     These  currents  of  polarization  are 
called  electrotonic  currents. 

The  electrotonic  current  excited  in  one  of  the  two  main  branches 


E. 

A      -. 

,^ 

J> 

^"-V- 

-t-  +  +  -*--(-  + 

4- 

+  -+   -1-  - 

^^-(§>-^' 


Fig.  56c. — Diagram  illustrating  the  position  of  the  ions  which  are  responsible 
for  the  direction  of  the  current  of  negative  polarization 
indicated  by  the   galvanometer,   G. 
When   ...o  current  ceases  to  flow  through  the  battery  circuit,  B,  the  col- 
lection of  a  larger  number  of  positive  ions  in  the  neighborhood  of  the  pole,  C, 
causes  the  current  to  flow  in  the  reverse  direction  through  the  galvanometer. 
The  plus  and  minus  signs,  D  and  E,  indicate  the  direction  of  extra  polar 
electrotonic  currents. 


of  a  sciatic  nerve  is  strong  enough  to  excite  an  effective  impulse 
in  the  other  branch.  This  effect  is  not  due  to  spreading  of  the 
current,  as  it  will  not  occur  if  the  stimulated  branch  is  crushed. 


THE  PERIPHERAL  NERVES 


CONDITIONS  AFFECTING  ELECTRICAL  STIMULATION  OF  THE  NERVES 


The  Speed  of  the  Make  or  Break  —  An  apparatus  has  been 
devised  which  depends  upon  the  rapid  or  slow  opening  of  a  shutter 
controlling  the  size  of  an  opening  between  two  concentrated  solu- 

98 


THE  NERVOUS  SYSTEM 


tions  of  zinc  sulphate  in  which  is  immersed  electrodes  of  zinc  and 
which  is  capable  of  more  rapidly  or  slowly  increasing  the  current. 
{Fig.  57.) 


J 


Fig.  57. — A,  Diagram  of  Rheonome.  By  means  of  the  shutter,  1,  the  speed 
of  the  make  and  break  of  the  current  between  the  electrolytes  in  the  two 
boxes,  2  and  3,  communicating  only  through  the  slit,  4,  may  be  varied. 

B,  Illustrating  the  galvanometer  records  of  the  change  of  the  current  obtained 
by  the  differences  of  the  speed  of  the  make  accomplished  by  the  Rheonome. 


The  excitatory  effect  varies  in  proportion  to  the: 

(1)  Intensity  of  the  current. 

(2)  And  with  certain  limitations  upon  the  rate  of  change 
of  the  current.  Rapid  alterations  in  the  current,  as  in  very  rapid 
alterations  of  the  induced  current,  are  ineffective.  It  is  for  this 
reason  that  the  high  voltage  of  the  Tesla  current  may  be  used  for 
therapeutic  effects  upon  the  human  being, 

100 


THE  NERVOUS  SYSTEM 

Waller's  Characteristic  —  The  optimum  rate  of  change  is 
known  as  Waller's  characteristic.  The  rate  of  change  may  be 
recorded  graphically  and  is  called  the  current  gratient. 

The  Duration  of  a  Current  which  is  used  to  produce  excitation 
also  bears  important  relations  to  the  strength  of  excitation.  This 
relation  may  be  investigated  by  first  ascertaining  the  minimal 
strength  of  current  necessary  to  produce  excitation  and  then  deter- 
mining how  much  the  current  must  be  increased  as  the  time  be- 
tween the  make  and  break  is  shortened  to  produce  the  same  con- 
traction. 

Keith  Lucas'  Characteristic  —  Keith  Lucas  has  used  as  a  second 
characteristic  that  duration  of  the  stimulus  which  will  just  pro- 
duce an  excitation  when  the  strength  of  a  minimal  effective  stimulus 
is  just  doubled.  Each  tissue,  muscle,  nerve  and  nerve  ending  as 
well  as  these  various  tissues  in  different  animals  have  all  their 
definite  various  characteristics. 

The  Effect  of  Temperature  upon  Excitability  —  Within  certain 
limits  the  excitability  of  a  nerve  may  be  increased  by  cooling. 
Thus  a  frog's  nerve  cooled  to  2°  C.  for  a  day  will  be  so  excitable 
that  simple  section  of  the  nerve  may  be  sufficient  to  throw  it  into 
a  tetanus.  This,  however,  is  only  true  for  mechanical  stimuli.  In 
the  case  of  electrical  stimuli  warming  of  the  nerve  increases  irri- 
tability and  cooling  diminishes  it  for  all  galvanic  or  induction 
shocks  of  less  duration  than  .005  of  a  second.  In  the  case  of 
skeletal  muscles  excitability  is  incrieased  by  cooling  for  all  forms 
of  stimuli. 

The  reason  why  the  time  of  .005  of  a  second  is  a  factor  in  the 
effect  of  temperature  on  irritability  is  because  the  temperature 
produces  two  effects  which  do  not  vary  at  the  same  rate  with 
changes  of  temperature.  Thus  cooling  of  a  nerve  both  delays  the 
subsidence  of  the  excitatory  process  and  renders  more  difficult  the 
initiation  of  the  excitatory  change,  but  the  delay  in  the  subsidence 
of  the  excitatory  process  reduces  the  amount  of  current  needed 
for  excitation  in  an  increasing  ratio  the  longer  the  duration  of  the 
current,  while  increasing  the  difficulty  of  the  initiation  of  the  exci- 
tatory process  such  as  is  produced  by  (1)  cooling,  (2)  prolonging 
the  current,  (3)  delaying  its  subsidence,  increases  also  the  current 
required  for  excitation  in  the  same  ratio,  or  in  an  exponential 
ratio  as  the  current  is  lengthened. 

102 


THE  NERVOUS  SYSTEM 

Effect  of  Injury  on  Irritability  —  Immediately  after  injury  a 
nerve  is  more  irritable  near  the  site  of  injury.  After  a  time  irri- 
tability diminishes  progressively  in  a  downward  direction,  so  that 
the  portion  nearest  the  muscle  is  longest  irritable. 

Direction  of  Conductivity  Across  the  Motor  End  Plate  —  The 
motor  end  plate,  or  the  interval  between  the  nerve  and  the  muscle, 
constitutes  a  true  synapse.  Conduction  across  it  is  only  possible 
in  one  direction.  This  is  proved  by  the  purely  local  contraction 
which  is  excited  by  snipping  a  nerve-free  portion  of  a  split  muscle 
and  contrasting  the  local  contraction  so  excited  with  the  contrac- 
tions in  both  split  portions  when  the  ends  of  the  nerves  in  one  half 
are  snipped. 

The  Specific  Delay  at  the  End  Plate  -—  A  certain  definite  period 
of  delay  exists  in  the  transmission  of  an  impulse  across  a  motor 
end  plate.  It  has  been  found  to  be  .0013  of  a  second.  The  motor 
end  plate  also  shows  fatigue  more  quickly  than  either  the  nerve 
or  muscle,  a  fact  also  indicated  by  the  specific  action  of  curare  and 
nicotine  upon  the  motor  end  plate. 

Action  of  Nicotine  —  Nicotine,  after  a  primary  stimulant 
action,  has  very  much  the  same  blocking  effect  upon  the  motor 
end  plate  that  curare  possesses,  though  it  is  much  less  powerful 
than  curare.  Four  mg.  of  nicotine  injected  into  the  veins  of  a 
anesthetized  fowl,  will  cause  a  tonic  contraction  of  all  the  muscles, 
a  phenomenon  which  may  be  immediately  set  aside  by  curare  and 
one  which  can  occur  when  enough  nicotine  has  been  given  to 
paralyze  all  the  motor  nerves,  or  after  all  the  motor  nerves  have 
degenerated  in  consequence  of  their  having  been  previously  sec- 
tioned. Thus  nicotine,  like  curare,  produces  its  effect  by  acting 
upon  the  substance  of  the  motor  end  plates. 

Specific  Optimal  Excitation  Time  of  the  Motor  End  Plate  — 
A  fourth  fact  demonstrating  the  different  essence  of  the  motor 
end  plate  is  its  different  optimal  excitation  time.  This  represents 
the  relation  of  the  strength  of  the  current  to  the  duration  of  the 
current  necessary  to  produce  contraction.  The  muscle  and  the 
nerve  and  motor  end  plate  all  possess  different  optimal  excita- 
tion times.  The  nerve-free  end  of  the  sartorious  possesses  an 
excitation  time  of  .017  seconds,  and  this  may  be  taken  as  the  excita- 
tion time  of  the  muscle. 

The  excitation  time  of  the  sciatic  nerve  trunk  is  about  .003 

104 


THE  NERVOUS  SYSTEM 

second,  and  possesses  a  steeper  gradient.  That  then  is  the  excita- 
tion time  of  nerve  fibers.  In  the  middle  of  the  sartorious  muscle 
of  the  frog,  in  the  region  of  the  motor  end  plate,  the  excitation  time 
is  .00005. 

The  Neuromuscular  Juncture  of  the  Sympathetic  Nerves  and 
the  Action  of  Adrenalin  upon  It  —  The  sympathetic  nerve  fibers 
end  seemingly  in  direct  contact  with  the  muscular  fibers,  v7ithout 
the  intermediation  of  any  motor  end  organ.  Nevertheless  there 
is  evidence  that  here  also  there  is  present  a  third  substance  dif- 
ferent from  the  nerve  and  muscle  vs^hich  bridges  the  gap  between 
the  two  though  it  has  not  organization,  at  least  of  a  motor  end  plate. 
Adrenalin  possesses  a  specific  stimulant  action  on  the  whole  of  that 
portion  of  the  sympathetic  nervous  system  which  causes  augmenta- 
tion of  function.  Hence  it  contracts  all  blood  vessels  supplied  by 
these  nerves.  Smooth  muscle  not  innervated  by  the  sympathetic 
nervous  system  as  that  of  the  blood  vessels  of  the  brain  and  lungs  is 
unaffected  by  the  injection  of  adrenalin.  Therefore  the  action  of 
adrenalin  cannot  be  upon  the  muscular  fiber  itself.  Adrenalin  is 
just  as  effective,  however,  after  complete  degeneration  of  the  post- 
ganglionic fibers  of  the  sympathetic  nerves,  so  that  its  action  cannot 
be  upon  these  post-ganglionic  fibers  themselves,  but  must  be  upon 
some  third  substance  intervening  between  this  fiber  and  the  muscle. 
The  same  substance  may  be  intermediary  in  all  synapses  and  closely 
allied  to  the  substance  of  the  motor  end  plate.  Its  similar  nature 
to  the  material  of  the  motor  end  plate  is  suggested  by  the  fact  that 
injections  of  adrenalin  act  variously  on  skeletal  muscle,  forming 
a  marked  contrast  to  barium,  which  stimulates  every  skeletal 
muscle  fiber  in  the  body,  acting  upon  them  directly. 

The  Facts  Indicating  the  Nature  of  an  Excitatory  Process  — 
By  the  following  facts  the  nature  of  an  excitatory  process  in  nerves 
is  indicated: 

(1)  The  dependence  of  irritability  of  a  nerve  upon  a  supply 
of  oxygen  demonstrating  that  there  is  an  expenditure  of  energy 
even  though  in  medullated  fibers  evidence  of  fatigue  is  absent. 
It  is  impossible  to  estimate  any  dissipation  of  energy  in  the  form 
of  heat.    Non-medullated  fibers  can  be  fatigued. 

(2)  The  failure  of  the  decrement  in  the  excitatory  process  as 
it  becomes  transmitted. 

(3)  The  excitatory  state  is  attended  with  an  electrical  change 

106 


THE  NERVOUS  SYSTEM 

of  such  a  nature  that  an  excited  spot  is  negative  to  all  other 
spots.  The  electrical  change  rises  to  a  maximum  rapidly  and  dies 
away  slowly.  The  amount  of  rise  and  fall  is  dependent  upon  the 
tissue  under  investigation. 

(4)  The  excitatory  change  is  aroused  only  at  the  poles  of  a 
current  passing  through  the  tissue,  i.e.,  at  the  places  where  the 
collection  of  ions  is  greatest. 

(5)  Excitation  occurs  only  at  the  cathode  at  the  make  and, 
only,  if  the  current  attains  sufficient  strength  within  a  certain 
length  of  time. 

(6)  All  living  tissues  are  made  up  of  colloids  divided  into 
compartments  by  membranes  of  various  permeabilities  and  perme- 
ated with  salts  and  various  electrolytes  in  solution.  Very  many 
possibilities,  therefore,  exist  for  the  formation  of  successive  com- 
partments characterized  by  large  differences  in  potential.  "We 
may  conceive  of  a  successive  transmission  of  such  electrical  states, 
and  of  such  a  movement  of  the  ions,  along  a  successive  series  of  com- 
partments in  a  nerve  fiber  as  will  account  for  large  differences  in 
potential.  The  process  may  be  roughly  likened  to  the  explosion 
of  a  successive  chain  of  equal  masses  of  gunpowder.  The  number 
of  variables  affecting  the  movement  of  the  ions  are  numerous  and 
will  permit  of  many  possibilities. 


108 


II 
THE  SPINAL  CORD 

MORPHOLOGY 

Its  Structure  from  a  Development  Standpoint  —  In  certain 
orders  of  invertebrates  the  whole  central  nervous  system  is  com- 
posed solely  of  ganglia  united  by  nerve  strands.  These  simpler 
nervous  systems  are,  therefore,  segmental  in  character.  Even  in 
the  embryo  of  mammals  the  first  traces  of  the  nervous  system  are 
segmental.  In  the  fully  developed  nervous  system  of  mammals  all 
trace  of  the  segmental  character  of  the  nervous  system  is  lost 
except  as  it  is  represented  by  the  regular  manner  in  which  the 
spinal  nerves  leave  the  spinal  cord. 

Gross  Anatomy  of  the  Spinal  Cord  —  The  spinal  cord  is  ap- 
proximately eighteen  inches  long.  (Fig.  58.)  From  its  lateral 
surfaces  are  given  off  thirty -one  pairs  of  nerves.  Each  pair  is  com- 
posed of  an  anterior  and  posterior  root  which  emerges  from  the 
spinal  canal  through  the  intervertebral  foramen.  On  each  posterior 
root,  before  it  joins  the  anterior  root  in  its  passage  through  the 
intervertebral  foramen,  is  a  large  ganglion  through  which  the  pos- 
terior root  passes.  The  anterior  roots  arise  by  a  series  of  fasciculi 
spread  out  over  a  rather  considerable  length  of  the  particular  level 
of  the  cord  from  which  the  root  arises.  The  posterior  root  arises 
as  a  single  well-marked  bundle. 

On  section  of  the  cord  it  is  seen  to  be  composed  of  a  peripheral 
white  substance  and  a  central  gray  substance.  The  central  gray 
substance  is  shaped  somewhat  like  an  H,  and  possesses  in  other 
words  two  anterior  horns  and  two  posterior  horns  connected  with 
a  transverse  bar  of  gray  matter.  (Fig.  59.)  In  the  center  of  this 
transverse  bar  is  a  central  canal.  The  white  matter  owes  its  color 
to  the  fact  that  it  is  composed  of  medullated  nerve  fibers.  The  gray 
matter  is  darker  because  within  it  are  contained  the  nerve  cells  of 
the  spinal  cord.    Each  lateral  half  of  the  spinal  cord  is  separated 

110 


THE  NERVOUS  SYSTEM 


Superior     peduncle    of 

the  cerebellum. 
Sulcus       longitudinalls 

medius. 
Glosso-pharyngeal. 
Vagus. 

Spinal  accessory. 


Ligamentum   denticula- 
tum. 


Posterior     longitudinal 
fissure. 


An  anterior  root. 
A  posterior  root. 


Fig,  58. — Dorsal  aspect  of  the  medulla  oblongata  and  spinal   cord  with  the  dure^ 
mater  partially  removed.    (Morris.) 


112 


THE  NERVOUS  SYSTEM 


114 


THE  NERVOUS  SYSTEM 


from  the  other  by  a  deep  anterior  and  posterior  fissure  which 
reaches  nearly  to  the  central  transverse  bar  of  gray  matter.    At  the 
bottom  of  these  fissures  are  strands  of  transverse  white  fibers. 
These  are  the  anterior  and  posterior  commissures.    The  amount 

of  central  gray  matter  at  any 
tJ^M-^^  level  of  the  spinal  cord  is  in 
proportion  to  the  number  of 
nerve  fibers  coming  off  at  that 
particular  level.  The  amount 
of  white  matter  diminishes 
progressively  from  above 
downwards.  The  size  of  the 
transverse  section  of  the  cord 
is  greatest  in  the  cervical  re- 
gion, that  region  supplying 
the  upper  limbs  and  contain- 
ing all  the  fibers  in  the  white 
matter  to  and  from  the  dorsal 
and  lumbar  regions  as  well. 

The  cord  is  smallest  in  the 
dorsal  region  and  again  en- 
larges in  the  lumbar  region 
though  smaller  here  than  in 
the  cervical  region.  The  en- 
largement in  the  lumbar  re- 
gion is  dependent  entirely 
upon  the  large  amount  of 
gray  matter,  the  axons  of 
which  supply  the  lower  limbs. 
(Fig.  60.) 

The  Group  of  Nerve  Cells 
—  The  nerve  cells  of  the  gray 
matter  are  collected  into  cer- 
tain groups.     (Fig.  61.)    Of  the  anterior  horn  there  are : 

1.  A  median  group.    Many  of  the  processes  of  this  group  cross 
the  middle  line. 

2.  An  external  group  of  large  multipolar  cells  whose  axons 
enter  directly  the  anterior  nerve  roots. 

3.  At  the  base  of  the  anterior  horn,  in  a  region  which  may  be 

116 


C 
C. 


P'ig.  60.— Sections  of  spinal  cord  in  lower 
cervical,  mid-thoracic,  and  mid- 
lumbar  regions.     (Quain.) 
On  the  right  side  of  each  section  con- 
ducting tracts  are  indicated.    P.-M .'  (in 
the  lumbar  region),  septo-marginal  tract. 


THE  NERVOUS  SYSTEM 


termed  the  lateral  horn,  is  a  group  of  small  cells  whose  fibers 
also  enter  the  anterior  nerve  roots,  forming  the  smaller  nerve  fibers 
of  these  roots  and  belonging  to  the  sympathetic  nervous  system. 

4.    In  the  posterior  horn  the  nerve  cells  are  more  scattered  but  a 
very  well-marked  collection  of  cells  exists  at  the  root  of  the  pos- 
terior horn  near  its  in- 
"^  ternal  side.    It  is  known 

as    Clark's    column    of 
cells. 

The  cells  of  the  gray 
matter  of  the  spinal  cord 
may  be  classified  from 
their  functional  stand- 
point as : 

1.  Motor  cells,  chief- 
ly the  a  n  t  e  r  o-lateral 
cells  and  the  cells  of  the 
anterior  horn, 

2.  Cells  of  the  col- 
umns. The  cells  of 
Clark's  column,  because 
their  axons  form  a  defi- 
nite column  in  the  lat- 
eral regions  of  the  white 
matter  of  the  spinal 
cord. 

3.  Commissural  cells 
whose  axons  cross  to  the 
opposite  side  of  the  cord. 

4.  Cells  of  Golgi, 
represented  by  a  large 

number  of  the  cells  of  the  posterior  horn  which  are  multipolar 
and  whose  axons  do  not  travel  far  from  the  cell  but  rapidly  break 
up  into  dendrites.  They  are,  therefore,  chiefly  associative  in 
function. 

Significance  of  the  Connections  of  the  System  of  Neurons  — 
For  a  proper  understanding  of  the  functions  of  the  spinal  cord  a 
knowledge  of  the  connections  of  the  tracts  which  form  systems  of 
neurons  is  absolutely  essential. 

118 


Fig.  61. — Diagram  showing  on  the  right  side 
the  "ascending"  and  on  the  left  side  the 

"descending"  tracts  in  the  spinal  cord. 
1,  Crossed  pyramidal;  2,  direct  pyramidal; 
3,  antero-Iateral  descending;  da,  bundle  of 
Helweg;  4,  prepyramidal ;  5,  comma;  6,  pos- 
tero-mesial;  7,  postero-lateral ;  8,  marginal; 
9,  dorsal  cerebellar;  10,  antero-Iateral  ascend- 
ing or  ventral  cerebellar;  s-m,  septo-marginal ; 
s.  p.  I.,  superficial  postero-lateral  fibres  (dorsal 
root-zone  of  Flechsig) ;  a  to  a^,  groups  of  cells 
in  the  anterior  horn;  i,  intermedio-lateral 
group  or  cell-column  in  the  lateral  part  of  the 
grey  matter;  p,  cells  of  posterior  horn;  d 
dorsal  nucleus  or  cell-column  of  Clark.  The 
dots  represent  "endogenous"  fibres  (arising  in 
grey  matter  of  cord)  having  for  the  most  part 
a  short  course. 


THE  NERVOUS  SYSTEM 


Methods  for  Tracing*  the  System  of  Neurons  — 

a.     By  intravital  staining. 

h.  By  the  impregnation  method  of  Golgi.  This  method  accom- 
plishes the  impregnation  of  the  neurons  by  a 
silver  salt  which  blackens  on  exposure  to  light. 
The  feature  which  makes  this  method  of  value 
is  the  fact  that  the  impregnation  is  not  general. 
In  virtue  of  this  fact  sections  of  considerable 
thickness,  containing  a  long  distance  of  any 
nerve  fiber,  may  be  studied. 

c.  Myelination  Method  —  As  the  nervous 
system  develops  the  nerve  fibers  become  inclosed 
in  their  myelin  sheaths.  The  various  systems  of 
neurons  do  not  acquire  their  sheaths  at  the  same 
period.  The  tracts,  which  develop  phylogeneti- 
cally  later,  that  is  the  youngest  tracts,  acquire 
their  myelin  sheaths  later  and  may  hence  be 
recognized  by  stains  which  bring  out  the  myelin 
sheath,  such  stains  when  applied  at  an  early 
period  of  their  development  failing  to  render 
them  conspicuous  as  compared  to  the  other  sur- 
rounding tracts. 

d.  The  Wallerian  Method  —  A  nerve  fiber 
which  is  divided  degenerates  away  from  the 
nerve  cell  of  which  the  fiber  may  be  an  axon. 
Whole  tracts  of  nerve  fibers  may,  therefore,  de- 
generate when  they  come  from  the  same  area  of 
gray  matter.  (Fig.  62.)  As  a  result  of  this 
degeneration  fatty  products  are  formed  in  the 
myelin  sheath  of  the  degenerated  nerves  which 
take  an  intense  black  stain  with  osmic  acid.  At 
a  period  of  three  weeks  after  the  tract  has  been 
divided  it  will  appear  black;  at  the  end  of  six 
months  these  products  will  be  removed  and  the 
degenerated  tract  will  take  no  stain  at  all.  At 
this  stage  it  will  also  contrast  strongly  with  the 

undegenerated  tracts  which  stain  normally.     (Fig.  63.) 

e.    Method  of  Retrograde  Degeneration  —  If  an  axon  is  divided 
at  a  point  distal  to  its  cell,  a  certain  degree  of  degeneration  will 

120 


Fig.  62. — Diagram 
showing  the  de- 
scending degen- 
eration of  the 
pyramidal  tract 
following  a  le- 
sion in  the  left 
c  e  r  e  b  r  o  hemi- 
sphere involving 
the  R  o  1  a  n  d  i  c 
area. 


THE  NERVOUS  SYSTEM 

appear  in  the  cell  for  a  period  of  a  few  weeks,  after  which  such  a 
cell  will  again  regain  its  normal  staining  power. 


Fig.  63. — Diagram  of  sections  of  the  spinal  cord  of  the  monkey,  showing  the 
position  of  degenerated  tracts  of  nerve-fibres  after  specific  lesions  of  the 
cord  itself,  of  the  afferent  nerve-roots,  and  of  the  motor  region  of  the  cere- 
bral cortex.  The  degenerations  are  sho-^Ti  by  the  method  of  Marchi.  The 
left  side  of  the  cord  is  in  all  cases  on  the  reader's  left  hand.     (Quain.) 

I.  Degenerations  resulting  from  extirpation  of  the  motor  area  of  the  cor- 
tex of  the  left  cerebral  hemisphere. 

II.  Degenerations  produced  by  section  of  the  dorsal  longitudinal  bundles 
in  the  upper  part  of  the  medulla  oblongata. 

III.  and  IV.  Results  of  section  of  dorsal  roots  of  the  first,  second,  and 
third  lumbar  nerves  on  the  right  side.  III.  is  from  the  segment  of  cord  be- 
tween the  last  thoracic  and  first  lumbar  roots;  IV.  from  the  same  cord  in  the 
cervical  region. 

V.  to  VIII.  Degenerations  resulting  from  (right)  semi-section  of  the  cord 
in  the  upper  thoracic  region.  V.  is  taken  a  short  distance  above  the  level  of 
section;  VI.  higher  up  the  cord  (cervical  region);  VII.  a  little  below  the 
level  of  section;  VIIL,  lumbar  region. 

122 


THE  NERVOUS  SYSTEM 

The  same  degenerative  changes  may,  however,  appear  in  a 
motor  cell  from  a  section  of  posterior  nerve  root.  Retrograde  de- 
generation is  probably,  therefore,  a  degeneration  of  disuse  and  must 
be  used  in  the  tracing  out  of  nerve  tracts  with  much  caution. 

PHYSIOLOGY 

THE  EFFERENT  AND  AFFERENT  PATHS  TO  AZSTD  FROM  THE  CORD 

The  Functions  of  the  Anterior  Nerve  Roots  and  Method  of 
Investigating  Them  —  If  the  anterior  nerve  root  is  divided  there 
will  result  a  paralysis  of  certain  muscles.  If  the  central  end  of 
the  root  is  stimulated  no  effects  will  be  produced.  If,  on  the  other 
hand,  the  peripheral  end  is  stimulated  certain  muscles  will  con- 
tract. 

If  the  anterior  root  is  one  of  the  thoracic  roots,  certain  visceral 
effects  will  be  produced  by  peripheral  stimulation.  Dilatation  of 
the  pupils,  or  constriction  of  certain  blood  vessels,  or  augmentation 
of  the  heart  beat,  are  among  these  visceral  effects. 

The  Functions  of  the  Posterior  Roots  —  Division  of  one  pos- 
terior nerve  root  will  usually  produce  no  noticeable  effect.  Stimu- 
lation of  its  peripheral  end  is  also  without  effect. 

Stimulation,  however,  of  its  central  end  in  the  conscious  animal 
will  produce  signs  of  pain.  If  the  spinal  cord  has  been  divided 
beneath  the  brain,  central  stimulation  will  produce  reflex  move- 
ments. If  two  or  three  posterior  nerve  roots  have  been  divided 
there  will  be  anesthesia  over  limited  areas  of  the  surface. 

The  anterior  roots  must,  therefore,  be  regarded  as  entirely 
efferent  in  their  function,  i.e.,  as  the  pathway  out  from  the  spinal 
cord,  the  posterior  roots  as  entirely  afferent  and  the  pathway  into 
the  spinal  cord. 

The  Peripheral  Distribution  of  the  Anterior  Roots,  and  the 
Function  of  the  Plexuses  —  Each  muscle  of  the  limbs  receives 
nerve  fibers  from  more  than  one  segment  of  the  spinal  cord.  Hence 
stimulation  of  one  anterior  nerve  root  in  a  peripheral  direction 
does  not  produce  contraction  of  any  one  muscle  or  one  physiological 
group  of  muscles.  The  anterior  nerve  roots  passing  from  that 
region  of  the  spinal  cord  which  supplies  the  limbs  unite  after  leav- 
ing the  spinal  cord  to  form  plexuses.     From  these  plexuses  the 

124 


THE  NERVOUS  SYSTEM 

single  nerves  come  off  which  supply  groups  of  muscles  which  are 
physiologically  related. 

Stimulation  of  one  of  these  nerves,  therefore,  causes  a  con- 
traction of  one  muscle  or  one  group  of  muscles  which  are  physio- 
logically related. 

The  Function  of  the  Fine  Fibers  —  A  section  of  a  thoracic 
anterior  nerve  root  shows  it  to  be  composed  of  large  ancl  small 
fibers.  The  large  fibers  are  axons  of  the  large  cells  in  the  lateral 
region  of  the  anterior  horn  and  run  to  the  muscles. 

The  fine  fibers  are  axons  of  the  cells  in  the  lateral  horns  and 
pass  as  the  white  rami  communicates  to  the  sympathetic  system. 
These  fibers  transmit  impulses  which  cause  dilatation  of  the  pupils, 
augmentation  of  the  heart  beat,  contraction  of  the  blood  vessels, 
inhibition  of  movements  of  the  intestines  and  erection  of  hairs. 

1.  The  Immediate  Fate  of  the  Fibers  of  the  Posterior  Nerve 
Roots  —  The  fibers  of  the  posterior  roots  pass  directly  into  the 
spinal  cord,  divide  into  an  ascending  bundle  and  descending 
bundle. 

(a)  Lissauer's  Column  —  The  descending  bundle  forms  a  tract 
near  the  tip  of  the  posterior  horn.  It  is  known  as  Lissauer's 
column.  The  fibers  of  this  tract  are  short  and  terminate  in  cells 
in  the  substantia  gelatinosa  at  the  tip  of  the  posterior  horn. 

(b)  The  Columns  of  Goll  and  Burdach  —  The  ascending  fibers 
are  long.  A  large  number  of  them  pass  upwards  in  the  posterior 
white  columns  of  the  cord,  i.e.,  in  the  region  between  the  posterior 
horns  and  the  posterior  median  fissure.  In  these  columns  the  fibers 
ascend  through  the  whole  length  of  the  cord,  and  as  they  ascend 
they  occupy  a  more  median  position,  making  room  in  this  manner 
laterally  for  other  fibers  entering  at  higher  levels.  (Fig.  64.)  The 
external  half  of  this  posterior  column  is  called  the  column  of  Bur- 
dach, the  internal  bundle  is  called  the  column  Goll.  Both  are  well 
marked  in  the  cervical  region.  Other  ascending  fibers  terminate  at 
different  levels  of  the  spinal  cord  around  cell  in  the  posterior  horn. 
All  of  the  long  fibers  give  off  collateral  fibers  to  cells  at  different 
levels  of  the  spinal  cord.  The  fibers  forming  these  long  tracts  are 
the  most  internal  of  the  fibers  of  the  posterior  root. 

(c)  Fibers  ending  in  the  cell  tracts  of  the  gray  matter.  These 
fibers  occupy  a  position  in  the  posterior  root  between  the  fibers 
of  the  long  posterior  columns  and  those  of  Lissauer's  column. 

126 


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THE  NERVOUS  SYSTEM 

Five  groups  are  traceable.     (Figs.  64,  66,  67  and  68.) 

1.     Fibers  to  the  cells  of  the  posterior  horn  of  the  same  side. 


Fig.  65. — Cross-sections  of  the  spinal  cord  of  the  dog  revealing  the  position 
of  the  nerve-tracts  descending  to  the  hind-limb  region  from  origin  in  the 
foremost  three  thoracic  segments,  by  the  method  of  "successive  degenera- 
tion." 

The  eighth  cervical  segment  had  been  exsected  and  568  days  later  a  crosscut 
was  made  at  the  hindmost  level  of  the  third  thoracic  segment.  The  trans- 
verse extent  of  this  lesion,  as  determined  by  microscopic  sections  afterwards, 
is  shown  in  diagram  1  of  the  figure.  The  greater  part  of  the  right  lateral 
column  is  seen  to  have  been  spared  from  injury.  Three  weeks  subsequent  to 
this  second  lesion  the  animal  was  sacrificed.  Preparations  made  with  the 
Marchi  method  for  revealing  degenerate  nerve  fibres  showed  the  degeneration 
indicated  by  diagrams  2,  3,  4  and  5  in  the  figure.  After  the  second  injury  to 
the  cord  the  scratch-reflex  remained  elicitable  from  the  right  shoulder,  but 
was  lost  from  the  left  shoulder  in  its  anterior  scapular  region.  The  degenera- 
tion of  these  proprio-spinal  fibres  descending  from  the  shoulder  segments  went, 
therefore,  hand  in  hand  with  disappearance  of  the  scratch-reflex  from  a  region 
of  skin  of  the  shoulder  whence  it  was  elicitable  previously.     (Sherrington.) 

130 


Si  5' 

Fig.  66. — Diagram  representing  the  manner  of  origin  or  termination  of  the 

roots  of  the  spinal  nerves  in  the  gray  matter  substance  of  the  spinal  cord. 

The  distribution  of  the  cells  of  the  gray  matter  and  the  tracts  of  nerve 
fibres  in  the  white  substance  of  the  spinal  cords: 

1.      THE  ROOTS 

r,  the  cells;  ra,  the  fibres  of  the  anterior  nerve  roots;  rpe,  external  trunk; 
rpi,  internal  trunk  of  a  posterior  nerve-root  with,  n,  collaterals  going  to  a 
posterior  external  group  of  cells  of  the  anterior  horn  and,  r,  to  a  group  an- 
terior to  the  latter;  ss,  to  posterior  horn  cells,  and,  t,  to  the  column  of  Clark. 

2.      THE   GRAY   MATTER 

a,  cells  of  the  lateral  column;  b,  cells  of  the  posterior  column;  c,  cells,  the 
axons  of  which  cross  the  white  commissure;  cp,  posterior  commissure;  d  (in 
the  substance  of  Rolando),  cells  of  Golgi  with  short  axons;  k,  cells,  the  axons 
of  which  cross  the  posterior  commissure  and  go  to  the  posterior  horn  of  the 
opposite  side;  r,  cells,  the  axons  of  which  turn  back  into  the  posterior  root 
zone. 

3.      COLUMNS  OF  THE  WHITE  MATTER 

al,  antero-lateral  column  or  the  column  of  Gowers;  am,  antero-marginal 
column  or  the  column  of  Loewenthal;  bpa,  bpm,  brs,  median  portion,  antero 
and  posterior  columns  of  Burdach;  cl,  direct  cerebellar  tract;  fb,  continuation 
of  the  posterior  longitudinal  bundle;  jbl,  fibres  of  the  lateral  column;  fga, 
fibres  descending  possibly  from  the  anterior  corpora  quadrigemina,  and  pass- 
ing across  the  base  of  the  commissure;  fl,  fibres  of  the  olivo-spinal  tract;  fla, 
fibres  of  the  anterior  columns;  fp,  fibres  of  the  antero-internal  column;  ft, 
fibres  of  the  prepyramidal  tract  of  Monokaw;  gi,  portion  of  the  column  of 
Goll  contiguous  to  the  dorsal  septums;  gl,  intermediate  zone  of  the  posterior 
column;  i,  fibres  of  the  median  or  deep  lateral  column;  I,  fibres  coming  from 
the  lateral  column  and  terminating  in  the  anterior  horn;  m,  fibres  from  the 
anterior  root  zone;  n,  fibres  from  the  deep  column  terminating  in  the  pos- 
terior horn;  p,  lateral  pyramidal  tract  containing  two  kinds  of  fibres;  p,  an- 
tero-pyramidal  tract;  cp,  ventral  zone  of  the  posterior  tract;  z,  external  or 
marginal  root  zone. 

132 


THE  NERVOUS  SYSTEM 

2.  Fibers  to  the  cells  of  the  posterior  horn  of  the  opposite 
side. 

3.  Fibers  to  the  median  group  of  cells  of  the  anterior  horn. 

4.  Fibers  to  the  cells  of  Clark's  column. 

5.  Fibers  to  the  motor  cells  of  the  anterior  horn. 
Significance  of  the  Distribution  of  the  Fihers  of  the  Posterior 

Nerve  Roots  —  Means,  therefore,  exist  by  which  an  incoming  im- 
pulse may  pass  upward  for  the  whole  length  of  the  spinal  or  down- 
wards or  upwards  for  several  or  many  segments  of  the  spinal  cord 
or  to  a  number  of  different  groups  of  nerve  cells  within  the  gray 
matter. 

2.  Intersegmental  Fibers  and  Their  Positions  (Fig.  65)  —  The 
fibers  passing  between  different  segments  of  the  spinal  cord  are  of 
much  importance.  Within  the  white  matter  of  the  spinal  cord  they 
occupy  the  following  regions: 

a.  In  the  lateral  columns  immediately  outside  the  central  gray 
matter  in  the  concavity  formed  by  the  two  horns. 

h.     Close  to  the  gray  matter  in  the  anterior  basic  bundle. 

c.  In  the  posterior  columns  the  following  three  situations :  (1) 
Close  to  the  tip  of  the  posterior  horn.  (2)  A  small  area  between 
the  columns  of  Goll  and  Burdach  —  the  comma  tract.  (3)  Close  to 
the  posterior  fissure,  the  septomarginal  bundle. 

d.  Mingled  with  the  fibers  of  the  pyramidal  tract. 


CONDUCTING   FUNCTIONS   OF   THE    SPINAL    CORD 

The  Spinal  Tracts  —  Functionally  similar  nerve  fibers  within 
the  spinal  cord  are  seldom  isolated.  Almost  all  run  in  bundles  with 
other  fibers  serving  the  same  functions.  Practically  all  nerve  fibers 
within  the  cord  are  connected  by  means  of  collateral  fibers  with 
nerve  cells  of  more  than  one  segment.  These  collateral  fibers,  unlike 
their  parent  fibers,  which  are  medullated,  have  no  medullary  sheath. 
The  single  axis  cylinder  lies  embedded  in  a  layer  of  myelin  sur- 
rounded immediately  by  neuroglia. 

The  various  bundles  of  the  spinal  cord  may  be  divided  into :  (1) 
Proprio-spinal  or  internuncial  fibers,  fibers  connecting  various 
levels  of  the  spinal  cord,  some  of  which  are  ascending  and  others 
descending.     (2)  Ascending  bundles.     (3)  Descending  bundles. 

134 


THE  NERVOUS  SYSTEM 

Some  of  the  proprio-spinal  tracts  have  already  heen  considered. 
Inasmuch  as  they  are  both  ascending  and  descending  we  will  de- 
scribe them  together  with  the  ascending  and  descending  tracts. 
(Figs.  61,  65  and  67.) 

Descending  Tracts  —  Pyramidal  Tracts  —  Found  immediately 
in  front  of  the  base  of  the  posterior  horns.  It  contains  fibers  which 
originate  in  the  nerve  cells  of  the  motor  area  of  the  cerebral  cortex 
and  run  without  interruption  through  the  cerebral  peduncles, 
through  the  pons  Varolii,  and  through  the  medulla,  where  they 
decussate  with  each  other  to  gain  the  opposite  side  to  enter  the 
pyramidal  tract  of  the  spinal  cord  and  terminate  by  a  terminal 
arborization  probably  directly  around  the  motor  cells  of  the  anterior 
horns  of  the  cord.  By  collaterals  they  communicate  with  the  cells 
of  several  levels. 

The  Prepyramidal  Tract  —  Situated  in  the  spinal  cord  immedi- 
ately in  front  of  the  pyramidal  tract.  It  begins  in  the  red  nucleus 
of  the  mid  brain.  The  tract  very  probably  represents  an  indirect 
cerebellar  spinal  tract,  in  other  words  it  continues  the  efferent  im- 
pulses from  the  cerebellum  through  the  superior  peduncles  through 
the  red  nucleus  to  the  spinal  cord. 

The  Y estibulo-Spinal  Tract  —  This  tract  establishes  connections 
between  the  higher  equilibrium  centers  and  the  spinal  cord.  It 
begins  in  the  cells  of  Deiter's  nucleus  of  the  medulla,  which  is  an 
important  substation  to  the  cerebellum.  The  fibers  of  the  vestibulo- 
spinal tract  are  scattered  in  the  antero-lateral  column. 

The  Olivo-Spinal  and  Thalamo-Spinal  —  Situated  opposite  the 
tip  of  the  anterior  horn.  It  begins  in  the  optic  thalamus  and  in 
cells  of  the  inferior  olivary  body.  The  latter  may  be  regarded  as  a 
substation  for  many  of  the  fibers  between  the  thalamus  and  the 
cord. 

Tract  of  Marie  —  A  proprio-spinal  tract,  serving  the  same  pur- 
pose as  the  posterior  longitudinal  bundle  to  be  studied  later  in  the 
brain.  Its  fibers  are  both  ascending  and  descending  and  scattered 
in  the  anterior  columns. 

Comma  Tract  —  In  the  interval  between  the  columns  of  Burdach 
and  Goll,  chiefly  descending  branches  of  the  entering  posterior 
spinal  nerves. 

Septo-marginal  —  Chiefly  proprio-spinal,  and  situated  adjacent 
to  the  posterior  portion  of  the  posterior  fissure. 

136 


THE  NERVOUS  SYSTEM 


j!    ^    o  -o  CNAJ+* 

IT*   to    (o  S>-*^^ 
r-.  (u   «,  5  ''  cj 


CO 
bi) 


138 


THE  NERVOUS  SYSTEM 

Ascending  Tracts  —  Posterior  Columns  —  Divided  into  the  col- 
umn of  Burdach,  the  postero-lateral,  and  the  column  of  Goll  or 
postero-median.  The  fibers  of  the  posterior  columns  are  derived 
from  ascending  divisions  of  the  entering  posterior  nerve  roots.  As 
these  enter  they  occupy  first  the  postero-lateral  column  but  become 
displaced  internally  by  similar  fibers  entering  at  higher  levels. 
Therefore  the  column  of  Burdach  of  the  lumbar  region  becomes  the 
column  of  Goll  in  the  cervical  region.  In  the  cervical  region  the 
column  of  Goll  contains  fibers  from  the  lower  extremities  and  the 
column  of  Burdach  the  fibers  from  the  upper  extremity.  They 
terminate  in  the  medulla  around  cells  of  the  nucleus  cuneatus  and 
nucleus  gracilis. 

The  Direct  or  Dorsal  Cerebellar  Tract  —  Situated  just  anterior 
to  the  outer  extremities  of  the  posterior  horns,  external  to  the 
pyramidal  tract.  It  may  be  viewed  as  one  of  the  two  afferent  spino- 
cerebellar tracts.  Its  fibers  originate  as  axons  of  the  cells  of  Clark's 
column,  and  run  up  to  the  corpus  restiforme,  then  entering  the 
inferior  cerebellar  peduncle. 

The  Anterior  or  Ventral  Cerehellar  Tract  —  Situated  anterior 
to  the  dorsal  cerebellar  tract,  between  it  and  the  bundle  of  Helweg. 
It  ascends  through  the  medulla  to  join  the  superior  cerebellar 
peduncle,  by  which  it  enters  the  cerebellum,  to  end  in  the  cells  of 
the  ventral  nuclei  of  the  superior  worm.  Inasmuch  as  this  tract 
does  not  increase  in  size,  as  it  ascends,  some  of  its  fibers  may  join 
the  dorso-cerebellar  tract  or  end  in  the  cord. 

Spino-Thalamic  —  Situated  just  internally  to  the  anterior  cere- 
bellar fibers,  forming  a  tract  which  is  often  described  as  one  tract 
with  the  anterior  cerebellar  tract — the  tract  of  Gowers.  It  ter- 
minates in  the  cells  of  the  anterior  corpora  quadrigemina,  but 
chiefiy  in  the  cells  of  the  optic  thalamus. 

Proprio-Spinal  Filers  —  Chiefly  the  ascending  fibers  of  the 
tract  of  Marie  in  the  antero-lateral  column. 

Functions  of  the  Various  Tracts  —  Motor  impulses  descend 
through  the  pyramidal  tracts,  and  the  indirect  or  crossed  pyramidal 
tracts,  immediately  lateral  to  the  anterior  fissure. 

Impulses  of  pain  both  superficial  and  deep  enter  through  the 
posterior  roots,  cross  immediately  to  the  other  side  of  the  cord  and 
ascend  in  the  internal  portion  of  Gowers'  tract  to  the  optic  thala- 
mus.    (Fig.  68.) 

140 


THE  NERVOUS  SYSTEM 


Impulses  of  heat  and  cold  follow  the  same  course. 

Impulses  of  touch  and  pressure  cross,  after  running  upwards 
for  a  few  segments  of  the  cord,  to  the  other  side  of  the  cord  and 
ascend  to  the  optic  thalamus  in  the  antero-lateral  column.  Some  of 
the  fibers  of  cutaneous  touch  particularly  those  of  tactile  discrim- 


ALS 


Fig.  68. — The  course  of  the  fibres  composing  the  posterior  root. 

I.  The  fibres  of  the  posterior  cohimns. 

II.  Fibres  making  connection  with  Clark's  column  and  continued  upward 
in  the  posterior  cerebellar  tract,  P.  C. 

III.  IV,  and  V.  Fibres  forming  connection  with  posterior  horn  cells  and 
continued  upward  in  the  anterior  cerebellar  tract,  AC,  conveying  heterolat- 
eral  unconscious  afferent  impulses  of  muscular  coordination  and  reflex  tone. 
G.,  Gowers'  column  transmitting  impulses  of  pain,  heat  and  cold.  A.L.S., 
Antero-lateral  ascending  sensory  tract  conveying  impulses  of  touch  and 
pressure. 

ination  travel  upwards  uncrossed  in  the  posterior  columns.  Con- 
siderable evidence  exists  that  touch  impulses  occupy  a  different 
course  than  pain  and  temperature.  We  must  regard  superficial 
touch  sensations  as  compounded  of  superficial  tactile  discrimina- 
tion and  superficial  pressure  sensation.  In  the  disease  of  syringo- 
myelia, the  senses  of  temperature  and  pain  are  affected  while  the 
sense  of  touch  is  not.    Moreover  unilateral  section  of  the  cord  does 

142 


THE  NERVOUS  SYSTEM 

not  completely  abolish  the  sense  of  touch  on  the  same  side  below  the 
level  of  the  lesion. 

Impulses  of  muscular  sensibility  may  be  divided  into  those 
which  reach  consciousness  and  those  which  do  not.  The  former  are 
all  homolateral  within  the  spinal  cord  and  make  up  the  posterior 
columns.  The  latter  are  partly  homolateral,  forming  the  direct  or 
posterior  cerebellar  tract,  and  partly  heterolateral,  forming  the 
anterior  cerebellar  tract. 

Unilateral  section  of  the  Cord  will  produce  the  following  symp- 
toms: 

Motor  paralysis  below  the  site  of  the  lesion  upon  the  same  side. 

Partial  loss  of  consciousness  of  the  position  of  the  limbs  below 
the  site  of  the  lesion  on  the  same  side. 

Complete  anesthesia  below  the  level  of  the  lesion  on  the  opposite 
side.  There  will  be  a  preservation  of  sensations  of  touch  and  pres- 
sure for  four  or  five  segments  below  the  level  of  the  lesion  on  the 
opposite  side.  There  will  be  slight  anesthesia  for  a  narrow  strip  at 
the  level  of  the  lesion  on  the  same  side.  This  narrow  zone  will  be 
above  a  hypergesthetic  zone. 

There  will  be  a  paralysis  of  the  vaso-motor  nerves  below  the 
level  of  the  lesion  on  the  same  side.  Vasomotor  impulses  travel 
down  the  cord  from  the  medulla  on  the  same  side. 

SPINAL   FUNCTIONS 

For  the  study  of  the  functions  or  reactions  of  the  spinal  cord 
a  study  of  the  cord  separated  from  the  brain  furnishes  much  valu- 
able information.  We  are  then  able  to  study  what  may  be  termed 
pure  spinal  reactions,  reactions  uninfluenced  by  impulses  contin- 
ually descending  from  above.  An  animal  in  which  the  spinal  cord 
has  been  severed  from  the  brain  is  called  a  spinal  animal. 

Spinal  shock  is  the  first  effect  of  dividing  the  spinal  cord. 
There  is  a  great  fall  in  the  blood  pressure  and  absolute  paralysis 
of  the  skeletal  muscles  and  of  the  sphincters  and  abolition  of  all 
reflexes. 

The  shock  appears  to  only  exist  aboral  to  the  plane  of  section. 
In  monkeys,  for  instance,  after  section  of  the  cord  below  the  cer- 
vical region,  though  there  is  a  fall  of  blood  pressure  and  paralysis 
of  the  trunk  and  lower  extremities,  nevertheless  all  muscles  sup- 
plied by  nerves  issuing  from  the  cord  above  the  plane  of  section 

144 


THE  NERVOUS  SYSTEM 


are  active.  Immediately  after  the  section  the  animal  will  gaze 
out  of  the  window  in  a  contented  manner  and  even  catch  at  flies. 
After  a  period,  which  is  proportional  to  the  height  in  the  scale 
of  life  which  the  animal  occupies,  recovery  from  the  shock  occurs. 
Permanent  paralysis  of  voluntary  motion  and  loss  of  sensation 
remains  for  all  regions  below  the  plane  of  section. 


Fig.  69. — Tracing  of  the  flexion  of 
the  hip  in  the  ''scratch-reflexJ' 
The  reflex  is  evoked  by  two  sepa- 
rate stimulations  (unipolar  faradiza- 
tion) at  points  ten  centimeters  apart 
on  the  skin  surface.  The  upper  sig- 
nal shows  the  time  of  application  of 
the  first  stimulation,  and  the  line 
immediately  below  that  the  frequency 
of  repetition  of  the  double  induction 
shocks  of  that  stimulation.  The  low- 
est line  signals  the  time  of  applica- 
tion of  the  second  stimulation;  the 
frequency  of  repetition  of  the  double 
shocks  in  this  stimulation  was  much 
greater  than  in  the  other  stimulation 
and  is  not  shown.  At  the  top  the 
time  is  marked  in  fifths  of  seconds. 
The  moment  of  commencement  of 
the  first  stimulation  is  marked  by  an 
abscissa  on  the  base  line.  The  pe- 
riods of  the  two  separate  stimula- 
tions overlap,  the  second  beginning 
a  full  second  before  the  first  ends, 
but  no  interruption  or  increase  of 
the  rate  of  rhythmic  reflex-response 
appears.     (Sherrington.) 


Recovery  from  the  Shock  —  From  the  shock,  however,  the 
animal  recovers.  The  blood  pressure  first  rises  to  normal.  The 
sphincters  become  functional  and  the  bladder  and  rectum  capable 
of  emptying  themselves.  Finally  muscular  tone  is  regained  and 
coordinated  movements  (reflexes)  may  be  excited  by  stimuli.  The 
first  reflexes  to  reappear  are  those  dependent  upon  painful  or 
nocuous  stimuli  and  later  those  reflexes  depending  upon  stimula- 
tion of  nerve  endings  in  the  joints  and  end  organs  in  the  muscles. 

Cause  of  Spinal  Shock  —  Spinal  shock  does  not  depend  upon 

146 


THE  NERVOUS  SYSTEM 

the  lowered  blood  pressure  nor  to  the  trauma  of  the  operation. 
Regions  not  in  the  shock  above  the  plane  of  section  are  exposed 
to  the  same  lowered  blood  pressure  and  a  second  section  below  the 
first,  even  if  performed  with  little  precaution  to  avoid  trauma, 


Fig.  70. — Flexion-reflex.    Spinal  dog.     Latent  time  of  incremental  reflex  com- 
pared with  that  of  initial  reflex.    Unipolar  faradization  by  break  shocks. 

Kathode  at  needle-point  in  plantar  skin  of  outermost  digit. 
A  weak  initial  stimulus  is  delivered  and  maintained,  and  then  when  the 
resulting  reflex  movement  has  become  steady  the  stimulus  is  increased  in 
intensity  by  short-circuiting  5  ohms  from  the  primary  circuit.  The  rate  and 
intensity  of  the  break  shocks  are  marked  above  by  a  recording  electromagnet ; 
the  armature  is  arranged  to  have  an  ampler  excursion  when  the  current  is 
increased  at  the  point  marked  B.  The  latent  time  of  the  incremental  reflex  is 
seen  to  right  hand,  and  is  di.stinctly  shorter  than  that  of  the  initial  reflex. 
Time  below  is  written  in  1/100  sec.  and  in  seconds.  Abscissae  on  the  myograph 
line  show  the  moment  of  first  delivery  of  the  initial  {A)  and  of  the  incre- 
mental (B)  stimuli.     (Sherrington.) 

does  not  add  to  the  degree  of  shock.  It  is  directly  dependent  upon 
the  cutting  off  of  the  normally  descending  impulses  from  higher 
parts  of  the  nervous  system  which,  so  to  speak,  keep  the  cord  awake 
and  responsive. 

Recovery  from  the  shock  depends  upon  the  power  of  the  spinal 
centers  to  acquire  a  more  independent  activity  of  their  own  in 

148 


THE  NERVOUS  SYSTEM 


the  absence  of  the  assistance  of  the  central  nervous  system.     In 
the  dog  recovery  may  even  occur  to  such  an  extent  that  it  may  be 

able  to  take  a  few  steps  if  it  be 
raised  and  given  a  push,  al- 
though it  cannot  walk. 

Swimming  movements  may 
be  carried  out  regularly.  They 
are  not  voluntary  but  purely  re- 
flex, the  necessary  sensory  stimu- 
lus being  supplied  by  the  exten- 
sion of  the  muscles,  and  are  of 
the  nature  of  alternate  flexion 
and  extension  in  the  hind  limbs 
when  the  animal  is  held  upright 
by  his  fore  limbs. 

A  Study  of  the  Spinal  Re- 
flexes —  Scratch  Reflex  —  Con- 
tinued gentle  stimulation  over 
the  shoulders  will  cause  rhyth- 
mic flexion  and  extension  of  the 
hind  limb  of  the  same  side  as 
though  making  an  attempt  to 
brush  off  the  irritant.  (Figs. 
69-71.) 

Sole  Reflex  —  Pricking  the 
sole  of  the  foot  will  cause  flex- 
ion of  the  leg  and  thigh  and,  if 
the  stimulus  is  strong  enough, 
extension  of  the  opposite  leg. 

Gentle  pressure  upwards 
against  the  sole  will  cause  ex- 
tension of  the  same  leg  and  flex- 
ion of  the  opposite  leg. 

Y oscular  Reflex  —  A  rise  in 
blood  pressure  may  be  obtained 
from  afferent  stimulation  of  the 
digital  nerve.     (Fig.  72.) 

Bladder  and  rectal  reflex  is 
the  stimulus  within  the  bladder 
150 


Fig.  71.— A,  B,  Scratch-reflex. 
The  tracings  show  the  usual  length- 
ening of  latency  on  reducing  the  in- 
tensity of  the  stimulation.  The  two 
tracings  are  in  reproduction  unequal- 
ly reduced,  but  the  frequency  of 
repetition  of  the  double-induction 
shocks  used  as  stimuli  was  the  same 
in  both  shocks  of  weaker  intensity  in 
B  than  in  A.  The  reflex  movement 
began  after  delivery  of  three  stimuli 
in  A,  after  delivery  of  nine  in  B. 
The  greater  intensity  of  the  stimuli 
in  A  is  also  evidenced  by  the  greater 
amplitude  of  the  movement  and  by 
the  longer  "after-discharge."  Time 
marked   in   fifths   of  seconds   below. 


THE  NERVOUS  SYSTEM 


and  rectum  of  urine  and  feces  which  will  cause  voluntary  evacua- 
tion of  these  organs.    Even  coitus  and  parturition  may  occur. 

Muscular  Tone  —  The  degree  with  which  muscular  tone  can 
return  is  illustrated  in  a  frog  which  has  recovered  from  spinal 
shock  by  section  of  its  posterior  spinal  nerves  on  one  side.  That 
side  will  then  be  perfectly  flaccid  and  completely  extended  con- 
trasting with  a  partially  flexed  position  of  the  other  leg  when  the 
animal  is  suspended,    (Fig.  73.)    In  other  words,  after  the  recovery 

from  the  shock  stim- 
uli are  continually  as- 
cending to  the  spinal 
cord  from  the  muscles 
themselves  which  ex- 
cite other  efferent 
stimuli  that  keep  the 
muscles  in  some  de- 
gree of  contraction. 
The  partial  contrac- 
tion, in  other  words, 
the  keeping  the  mus- 
cles in  a  condition  of 
wakefulness,  is  called 
tone. 

Tendon  Reflexes  — 
The  patella  reflex  is 
only  one  of  various 
other  tendon  reflexes, 
indeed  the  phenome- 
It  illustrates  the  factors  determin- 


Fig.  72. — Spinal  vasomotor  reflex;  dog;  300  days 
after  spinal  transection  at  eighth  cervical  level; 
chloroform  and  curare.  Electrical  stimulation 
of  central  end  of  a  digital  nerve  of  hind  limb 
during  the  time  marked  by  signal  on  second 
line  from  bottom.  The  arterial  pressure  (caro- 
tid) rises  from  90  mm.  Hg.  to  208  mm.  Hg. 
Time  marked  below  in  2  seconds.   (Sherrington.) 


non  is  common  to  all  tendons, 
ing  muscular  tone. 

A  tendon  reflex  may  be  elicited  by  tapping  the  tendon  of  a 
limb  placed  in  a  flexed  condition  but  preferably  in  such  a  position 
that  the  tendon  is  somewhat  on  the  stretch.  For  the  right  patellar 
reflex  the  right  knee  should  cross  the  left  allowing  the  leg  to  hang 
loosely  over  the  left  one.  The  patellar  tendon  is  then  sharply 
struck.  Immediately  the  quadriceps  extension  of  the  right  limb 
will  contract,  causing  the  leg  to  give  a  little  jerk.  The  latent 
period  between  the  time  of  the  blow  to  the  tendon  and  the  con- 
traction is  very  short,  according  to  Gotch  only  .005  of  a  second, 

152 


THE  NERVOUS  SYSTEM 


which  is  also  the  duration  of  the  latent  period  when  the  vastus 
internus  is  directly  stimulated. 

Manifestly,  therefore,  it  must  ht  considered  possible  that  the 
cause  of  the  knee  jerk  is  the  direct  effect  of  the  blow  upon  the 
muscle,  but  this  cannot  be  all.  Section  of  the  posterior  nerve  roots 
of  the  third  and  fourth  lumbar  nerves  will 
abolish  the  knee  jerk,  so  also  stretching  the 
hamstring  muscles  or  the  antagonists  of  the 
flexors  or  weak  stimulation  of  the  nerve  sup- 
plying hamstrings. 

Section  of  the  hamstrings  or  their  nerve 
will  increase  the  knee  jerk  reflex.  These  facts 
indicate  that  an  afferent  path  to  the  spinal 
cord  is  necessary  for  the  elicitation  of  the  ten- 
don phenomenon,  and  also  a  relaxation  of  the 
antagonists  to  the  muscles  which  produce  the 
contraction  of  the  muscles  which  are  con- 
cerned in  the  tendon  reflex  in  question. 

In  order  to  accomplish  this  relaxation, 
a  reflex  arc  through  the  spinal  centers  is  nec- 
essary, a  fact  also  attested  by  the  abolition  of 
the  knee  jerk  in  consequence  of  dividing  the 
posterior  spinal  roots. 

It  has  been  suggested  that  the  part  played 
by  the  spinal  cord  is  one  merely  maintain- 
ing muscular  tone,  keeping,  so  to  speak,  the 
muscles  in  a  state  of  wakefulness.  While  this 
suggestion  may  in  a  large  part  explain  the 
characters  of  the  tendon  reflex,  it  is  not  the 
entire  explanation.  More  accurate  measure- 
ments by  Jolly  of  the  current  of  action  in 
the  muscles  and  nerves,  with  a  sensitive  gal- 
vanometer, show  in  disagreement  with  the 
conclusions  of  Gotch  that  the  latent  period 
of  the  knee  jerk  contains  also  a  small  reduced 
reflex  time  of  .002  of  a  second,  corresponding  perhaps  with  only 
one  synapse.     These  measurements  are  as  follows: 


Fig.  73.— Illustrating 
the  difference  in  the 
tone  of  the  legs  of 
a  frog  when  the  pos- 
terior root  nerves 
of  one  side  have 
been  divided. 


154 


THE  NERVOUS  SYSTEM 

Time  of  knee  jerk 0053 

Time  in  afferent  ending 0004 

Time  in  nerve  conduction .0014 

Time  in  motor  endings 0013     .0031 


.002  + 


Other  examples  of  tendon  reflexes  are  the  Babinski  sole  reflex 
and  Koernig's  sign. 

These  facts  are  all  confirmed  by  certain  pathological  conditions 
in  man. 

In  locomotor  ataxia,  in  which  there  is  degeneration  of  the 
posterior  columns  of  the  spinal  cord  containing  the  mechanism 
for  afferent  impulses  from  the  muscles,  there  is  a  loss  of  knee  jerk. 
In  the  disease  lateral  sclerosis,  in  which  the  pyramidal  tracts  are 
degenerated,  there  no  longer  exists  any  controlling  influence  from 
above  upon  the  motor  mechanism  of  the  cord  and  the  motor  mech- 
anism of  the  cord,  as  in  recovery  from  spinal  shock,  assumes  an 
independent  and  exaggerated  activity,  consequently  the  knee  jerks 
are  increased. 


SUMMARY  OF  THE  FUNCTIONS  OF  THE  SPINAL  CORD 

The  spinal  cord  must,  therefore,  be  viewed  as  a  part  of  a  mech- 
anism for  obtaining  a  certain  definite  coordinated  response  of  a 
limited  segmental  character  from  certain  peripheral  stimuli  and 
for  maintaining,  as  a  result  of  certain  deep  seated  stimuli,  a  mus- 
cular tone  in  the  skeletal  muscles.  It  also  maintains  a  tone  in 
certain  of  the  vessels  and  structures  within  the  body  cavities  con- 
veniently though  not  accurately  described  as  visceral  tone. 

The  maintenance  of  both  the  skeletal  tone  and  visceral  tone  is 
part  of  a  reflex  mechanism  and  is  absent  in  the  absence  of  the 
necessary  afferent  impulses  or  is  changed  with  a  change  in  the 
normal  relation  of  excitatory  or  inhibitory  impulses  from  above 
or  from  other  parts  of  the  nervous  system. 

The  Characteristics  of  a  Spinal  Reflex  —  Purpose-like  —  Every 
reflex  movement  may  be  described  as  a  purpose-like  movement  for 
the  simple  reason  that  every  reflex  is  an  action  frequently  used  by 
the  animal.    This  fact  constitutes  the  reason  why  during  the  process 

156 


THE  NERVOUS  SYSTEM 

of  development  the  various  neurons  are  so  connected  that  the 
various  reflexes  become  possible.  The  word  purpose-like  has  been 
used  instead  of  purposeful  because  every  reflex  act  is  at  the  same 
time  fateful. 


Fig.  74. — A:  The  "receptive  field,"  as  revealed  after  low  cervical  transection, 
a  saddleshaped  area  of  dorsal  skin,  whence  the  scratch-reflex  of  the  left 
hind  limb  can  be  evoked.    Ir  marks  the  position  of  the  last  rib. 

B:  Diagram  of  the  spinal  arcs  involved.  L,  receptive  or  afferent  nerve-path 
from  the  left  foot;  R,  receptive  nerve-path  from  the  opposite  foot;  Ra,  Rb, 
receptive  nerve-paths  from  hairs  in  the  dorsal  skin  of  the  left  side;  FC, 
the  final  common  path,  in  this  case  the  motor  neurone  to  a  flexor  muscle 
of  the  hip;  Pa,  Pb,  proprio-spinal  neurones.     (Sherrington.) 


Fateful  —  The  spinal  cord,  unless  inhibited  by  actions  of  the 
higher  nervous  system,  always  responds  in  a  definite  calculable 
manner.  The  beheaded  eel  will  wind  itself  around  a  red  hot  poker. 
The  beheaded  snake  will  spring  back  to  any  agent  grasping  its 
tail. 

158 


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160 


THE  NERVOUS  SYSTEM 

Pleurisegmental  —  All  reflex  movements  are  such  as  would 
under  usual  conditions  perform  useful  acts  for  the  animal,  and  all 
are  complicated,  involving  several  segments  of  the  spinal  cord. 
They  are  all  pleurisegmental  (see  Fig.  74) . 

Capable  of  Spreading  —  The  plantar  or  sole  reflex  in  the  mam- 
mal not  only  involves  the  extremity  on  the  side  of  the  provoked 
sensory  stimulus  but  may  also  involve  the  extremity  of  the  other 
side. 

The  spreading  of  the  response  is  always  in  a  definite  order 
called  irradiation,  and  just  what  response  is  called  forth  is  deter- 
mined by  the  place  or  lociis  of  the  peripheral  stimulus.  We  have 
thus  far  only  spoken  of  the  contraction  of  certain  sets  of  muscles 
in  the  description  of  this  response,  but  the  contracting  muscles  are 
only  half  of  those  which  participate  in  the  reflex  act. 

Capable  of  Inhibition  —  No  reflex  can  effectively  take  place 
without  the  simultaneous  relaxation  of  the  set  of  muscles  antagon- 
istic to  those  which  are  undergoing  contraction.  During  the  re- 
flex withdrawal  of  one  foot  (flexion)  and  extension  of  the  oppo- 
site leg,  there  is  not  only  contraction  of  the  flexors  but  also  relaxa- 
tion of  the  extensors  on  the  one  side  and  contraction  of  the  exten- 
sors and  relaxation  of  the  flexors  on  the  other  side.  This  relaxa- 
tion is  accomplished  by  impulses  which  inhibit  centrally  the  im- 
pulses responsible  for  the  normal  muscular  tone  of  the  relaxing 
muscles.  The  relaxation  may  be  measured  by  a  recording  instru- 
ment which  demonstrates  the  actual  lengthening  of  the  muscle. 

A  reflex  action  may  be  altogether  prevented  by  influences 
transpiring  in  other  portions  of  the  central  nervous  system.  Any 
inhibition  is  accomplished  by  nerve  fibers  running  to  the  central 
synapses  of  the  reflex  in  question  from  the  other  portions  of  the 
nervous  system.  Certain  reflexes  are  prepotent ;  others  may  be 
made  prepotent  by  strong  stimuli.  Prepotent  reflexes  have  a 
tendency  to  inhibit  other  reflexes  which  may  be  transpiring. 
The  possibility  of  reinforcing  the  knee  jerk  reflex  by  pulling  apart 
the  clasped  hands  illustrates  the  presence,  normally,  of  constant 
inhibitory  impulses  to  the  extensors  of  the  thigh.  If  the  reinforc- 
ing act  precedes  the  stimulation  of  the  reflex  by  .06  see.  the  inhibi- 
tion begins  to  appear. 

Capable  of  Prepotency  —  Certain  reflexes  possess  precedence 
over  others.    Reflexes  from  painful  or  nocuous  stimuli  will  proceed 

162 


THE  NERVOUS  SYSTEM 


in  the  place  of  other  reflexes  which  may  have  been  started.  Only 
one  reflex  can  proceed  at  a  time.  The  central  nervous  system  only 
attends  to  one  thing  at  a  time.  A  reflex  in  process  of  performance 
will  be  checked  by  another  reflex  started  by  a 
stronger  stimulus.  The  checking  process  is 
one  of  inhibition,  but  after  the  period  of  in- 
hibition has  passed  the  inhibited  reflex  will 
proceed  again  with  renewed  vigor,  as  though 
its  stimulus  during  the  period  of  inhibition 
were  really  effective  though  apparently  only 
accumulatively  so. 

Capable  of  Beenforcement  —  If  one  reflex 
is  proceeding,  another  reflex  giving  rise  to  an 
action  cooperating  toward  the  same  end  is 
started,  will  proceed  and  strengthen  the 
first  reflex.  Strongly  pulling  the  interlocked 
fists  apart  will  reinforce  the  knee  jerk. 

Capable  of  Fatigue  —  Too  frequent  excita- 
tion of  a  reflex  causes  fatigue  at  the  central 
synapse.  If  the  stimulus  exciting  a  reflex 
which  has  been  fatigued  is  moved  only  a  very 
slight  distance  to  the  side  of  the  locus  of 
the  reflex,  it  will  again  proceed  with  renewed 
vigor.  Therefore  the  most  important  site  of 
the  fatigue  must  lie  in  the  synapse  upon  the 
afferent  side  of  the  reflex  arc. 

Explanation  of  the  "Mark  Time"  Move- 
ment —  Just  as  repetition  of  a  reflex  causes 
fatigue,  so  inhibition  causes  reenforcement  of 
a  reflex.  These  two  facts  explain  the  auto- 
matic swimming  movement  or  the  automatic 
and  continuous  flexion  and  extension  of  first 
one  leg  and  then  the  other  in  the  suspended 
dog.  The  weight  of  one  leg  produces  a  stimu- 
lus to  the  contraction  of  its  flexors,  accompanied  by  inhibition  of 
flexion  upon  the  opposite  side.  This  flexion  is  followed  by  slight 
fatigue  on  the  newly  flexed  side  and  a  dropping  of  the  inhibited 
side,  which  in  turn  is  stimulated  by  this  drop  or  extension  and, 
in  virtue  of  the  rest  during  the  previous  period  of  inhibition,  is 

164 


Fig.  75.  —  Scratch-re- 
flex interrupted  by 
a  brief  flexion-re- 
flex. 

The  time  of  appli- 
cation of  the  stimulus 
evoking  scratch-reflex 
is  shown  by  the  low- 
est signal  line ;  that  of 
the  stimulus  of  the 
flexion-reflex  in  the 
signal  line  immediate- 
ly above  the  other. 
Time  marked  in  fifths 
of  seconds  at  top  of 
the  record.  The 
scratch-reflex  returns 
with  increased  inten- 
sity after  the  inter- 
ruption. (Sherring- 
ton.) 


THE  NERVOUS  SYSTEM 

in  a  condition  to  respond  to  the  stimulus  produced  by  its  own 
extension.  This  stimulus  causes  it  to  be  flexed  and  the  flexion  in 
the  flrst  limb  to  be  inhibited  in  its  turn. 

In  the  excitation  and  control  of  reflex  actions  two  varieties  of 
afferent  impulses  are  concerned.    One  set  of  these  impulses  comes 


Fig.  75%. — Diagram  indicating  connections  and  actions  of  two  efferent  root- 
cells,  a  and  a'  in  regard  to  their  reflex  influence  on  the  extensor 
and   flexor   muscles    of   the   two   knees. 
a,  root-cell  afferent  from  skin  below  knee;  a',  root-cell  afferent  from  flexor 
muscle  of  knee,  i.e.,  in  hamstring  nerve;   e  and  e',  efferent  neurones  to  the 
extensor  muscles  of  the  knee,  left  and  right;  s  and  s',  efferent  neurones  to  the 
flexor  muscles;  E  and  E',  extensor  muscles;  F  and  F',  flexor  muscles.     The 
"schalt-zellen"    (v.    Monakow)    probably   between    the   afferent   and   efferent 
root-cells   are   for   simplicity    omitted.     The   sign    +    mdicates   that    at   the 
synapse  which  it  marks  the  afferent  fibre  a  (and  a')  excites  the  motor  neu- 
rone to  discharging  activity,  whereas  the  sign  —  indicates  that  at  the  synapse 
which  it  marks  the  afferent  fibre  a  (and  a')  inhibits  the  discharging  activity 
of  the  motor  neurones.    The  effect  of  strychnine  and  of  tetanus  toxin  is  to 
convert  the  minus  sign  into  plus  sign.     (Sherrington.) 

166 


THE  NERVOUS  SYSTEM 

from  the  surface  and  may  be  termed  exogenous  afferent  impulses. 
The  second  set  originate  within  the  muscles  themselves  and  within 
the  tendons  and  joints.    They  are  the  deep  or  endogenous  impulses. 

The  first  set  are  chiefly  concerned  in  the  excitation  of  reflexes. 
The  second  set  chiefly,  though  by  no  means  exclusively,  with  the 
degree  with  which  the  response  to  any  particular  reflex  takes  place 
in  the  various  muscles  concerned. 

In  other  words  the  second  set  of  impulses  guide  or  control  the 
response  in  such  a  manner  that  it  is  possible  for  it  to  become  a 
coordinated  movement.  It  is  through  them  that  information  is  ob- 
tained as  to  the  degree  of  contraction  of  any  muscle. 

When  these  impulses  are  cut  off  the  position  of  the  limbs  be- 
comes abnormal.  It  is  due  to  this  fact  that  after  the  posterior  nerve 
roots  of  one  hind  limb  of  a  frog  have  been  divided  the  frog's  limb 
assumes  a  position  of  permanent  extension  and  will  hang  with  the 
legs  limp. 

If  all  the  posterior  nerve  roots  of  the  cervical  nerves  of  one  side, 
except  the  eighth,  of  a  monkey  are  divided  the  monkey  will  still 
use  its  arm  for  climbing,  but  the  movements  will  be  inexact.  The 
inexactness  is  chiefly  in  the  arm.  The  hand,  which  is  supplied  by 
the  eighth  cervical,  exercises  perfect  precision.  The  monkey  has 
lost  information  from  the  muscles  enabling  it  to  know  the  various 
degrees  of  contraction  of  the  muscles  of  the  arm.  If  the  eighth 
cervical  nerve  is  then  also  divided,  the  arm  will  become  totally 
paralyzed. 

Capable  of  Localization  —  With  the  same  certainty  that  a  defi- 
nite muscle  contracts  after  the  application  of  a  stimulus  to  its  motor 
nerve,  so  the  application  of  a  stimulus  to  the  peripheral  ter- 
mination of  a  sensory  nerve  will  call  forth,  in  the  absence  of  in- 
hibitory influences,  a  definite  response.  A  fixed  path  of  least  re- 
sistance for  the  propagation  of  the  impulse  to  and  through  and 
from  the  central  nervous  system  has  been  developed. 

Capable  of  Delay  —  No  response  to  a  stimulus  of  a  sensory 
neuron  is  immediate.  A  delay  exists  which  represents  the  time 
necessary  for  the  impulse  to  ascend  the  sensory  neuron  and  for  the 
impulse  to  pass  across  the  synapse  in  the  central  nervous  system 
and  for  the  terminally  provoked  impulse,  the  efferent  impulse,  to 
descend  the  motor  or  secretory  nerve. 

The  speed  of  impulse  along  nerve  fibers  is  known  and  the  latent 

168 


THE  NERVOUS  SYSTEM 

period  involved  in  the  starting  of  the  sensory  impulse  and  in  the 
production  of  the  effect  by  the  efferent  impulse,  after  the  latter 
has  reached  the  peripheral  termination  of  the  efferent  nerve,  are 
also  known.  When  the  time  taken  by  these  processes,  which  rep- 
resents all  the  time  of  that  portion  of  a  reflex  occurring  outside 
the  central  nervous  system,  is  subtracted  from  the  total  time  of 
the  simplest  unilateral  reflex  act,  there  will  be  left  over  .008  of  a 
second. 

This  time,  therefore,  represents  the  time  of  that  portion  of  a 
reflex  act  which  is  occupied  in  the  passage  of  its  impulse  across 
the  synapses  in  the  central  nervous  system.  It  is  called  the  reduced 
reflex  time.  When  the  reflex  is  a  crossed  reflex  the  reduced  reflex 
time  is  .004  of  a  second  longer.  Probably  two  additional  synapses 
are  involved  in  a  crossed  reflex,  so  that  the  time  occupied  in  a 
single  synapse  is  about  .002  of  a  second. 

Capable  of  Summation  —  To  produce  a  reflex  response  by  a 
single  stimulus  that  stimulus  must  possess  a  certain  strength.  A 
weaker  stimulus  is  a  subminimal  stimulus,  A  subminimal  stimulus, 
however,  is  not  necessarily  without  effect,  inasmuch  as  several, 
five  or  six,  subminimal  stimuli  applied  at  a  proper  interval  will 
result  in  a  response.  The  term  summation  is  applied  to  this  phe- 
nomenon. 

Capable  of  Block  —  Fatigue  illustrates  one  form  of  block, 
Qamely,  an  increased  resistance  across  a  synapse.  The  existence 
of  a  definite  path  for  each  reflex  through  the  central  nervous  system 
demonstrates  the  presence  of  increased  resistance  to  that  reflex  in 
all  other  synapses  of  the  central  nervous  system.  The  reality  of  this 
increased  resistance  is  made  more  evident  when  it  is  dissipated  by 
the  administration  of  strychnine  or  the  tetanus  toxine. 

Capable  of  Facilitation  —  Some  resistance  to  the  passage  of  an 
impulse  across  the  central  synapse  of  a  reflex  exists  even  in  that 
synapse  which  belongs  peculiarly  to  the  reflex  in  question.  This 
resistance  can  be  measured  by  the  strength  of  current  necessary  to 
provoke  the  reflex.  It  may  be  diminished  by  frequently  provoking 
the  reflex  at  an  interval  not  short  enough  to  result  in  fatigue. 
This  diminution  of  resistance  across  a  synapse  by  use  is  called 
facilitation.  Upon  it  depends  the  possibility  of  education  and 
memory. 

The  Nature  of  the  Path  Across  a  Synapse  —  The  transmission 

170 


THE  NERVOUS  SYSTEM 

of  impulses  so  constantly  in  definite  paths  suggests  the  existence 
of  a  direct  connection  across  the  synapse.  Certain  observers  have 
found  good  evidence  of  such  direct  connections  among  some  of 
the  lower  orders  of  invertebrates  and  have  maintained  that  they 
exist  also  throughout  the  nervous  systems  of  animals.  By  special 
staining  methods  they  have  attempted  to  demonstrate  actual  con- 
nections between  the  dendrites  of  a  nerve  cell  at  nodal  points  in 
the  terminal  arborization  of  the  afferent  nerve  fiber  to  this  cell. 
In  fact,  some  preparations  show  that  the  terminal  arborization 
around  a  central  nerve  cell  forms  an  actual  basket  of  a  netlike 
structure  closely  surrounding  the  cell  with  enlarged  nodal  points. 
Do  the  fibrillge  of  the  nerve  cell  run  out  into  the  dendrites  and 
connect  by  means  of  them  with  these  nodal  points?  The  indirect- 
ness of  such  a  path  through  a  synapse  may  account  for  certain 
phenomena,  such  as  delay  existing  at  a  synapse,  but  the  law  of 
forwai'd  direction  will  ever  constitute  an  objection  to  the  existence 
of  a  direct  connection  across  a  synapse. 

There  must  exist  a  free  ending  to  the  dendrites  of  one  neuron, 
and  a  beginning  to  the  dendrites  of  the  neuron  next  in  the  chain, 
and  an  interval  filled  with  a  different  substance  between  the  two. 

Functions  of  the  Various  Portions  of  a  Reflex  Arc  —  The  func- 
tion of  the  nerve  fiber  is  solely  one  of  conduction.  We  may  exclude 
excitation. 

The  function  served  by  the  synapse  is  also  one  of  conduction. 

What,  however,  is  the  function  of  the  central  nerve  cell  ?  May 
it  originate  impulses,  or  does  it  modify  them,  or  does  it  solely 
conduct  them,  and  are  there  any  other  possible  functions  which  it 
may  perform? 

The  Function  of  the  Central  Nerve  Cell  —  In  answering  this 
question  all  the  vital  phenomena  presented  by  living  cells  must 
be  considered.  Foremost  among  these  is  the  maintenance  of  nutri- 
tion. We  have  seen  that  no  cell  is  capable  of  continued  existence 
without  a  nucleus.  The  sole  purpose  for  which  the  nervous  system 
has  developed  is  one  of  communication.  This  is  accomplished  by 
nerve  fibers.  Each  nerve  fiber  which,  in  many  instances,  consti- 
tutes the  major  part  of  the  neuron,  would  be  without  a  nucleus 
were  it  not  for  its  attachment  at  one  end  to  the  nerve  cell. 

Trophic — In  fact,  the  nerve  fiber  may  be  viewed  as  a  long  and 
permanent  pseudopod  of  a  nerve  cell,  and  without  attachment  to 

172 


THE  NERVOUS  SYSTEM 

the  cell  will  degenerate.  An  important  function,  therefore,  of 
the  nerve  cell  is  the  nutrition  of  its  nerve  fiber.  The  adjective 
trophic  is  the  term  which  is  used  to  describe  this  function. 

Transmission  —  Nerve  cells  must  transmit  impulses.  Less  cer- 
tainty, however,  attaches  itself  to  the  question  whether  nerve  cells 
modify  impulses  passing  through  them  apart  from  other  influences 
reaching  them  or  even  wJiether  they  may  be  spoken  of  apart  from 
the  fact  that  they  are  situated  at  a  synapse  as  switch  stations  of 
the  nerve  impulses. 

Automaticity  —  Much  evidence  exists  that  nerve  cells  do  not 
originate  nerve  impulses.  In  the  absence  of  all  afferent  stimuli 
they  become  functionless.  Metabolic  activity  with  the  evolution 
of  energy  transpires  within  them.  The  evidence  of  this  is  supplied 
by  the  rapid  loss  of  power  to  functionate  in  the  absence  of  oxygen. 

Clamping  the  aorta  soon  produces  a  paralysis  of  the  whole 
spinal  cord.  Nevertheless,  in  the  same  manner  a  lack  of  oxygen 
will  render  nerve  fibers  incapable  of  conduction. 

In  some  of  the  lower  invertebrates  the  ganglion  cells  of  afferent 
fibers  may  be  excised  without  injury  to  the  terminal  arborization 
of  the  afferent  and  efferent  nerve  fibers  to  these  cells  and  without 
immediately  influencing  in  any  way  the  function  of  the  concerned 
neurons.  So  far,  therefore,  as  the  nervous  activity  of  these  cells 
is  concerned  it  is  limited  entirely  to  transmission  and  trophic  func- 
tions. Like  other  cells  in  the  body  the  nerve  cells  have  become 
highly  differentiated  for  the  purpose  of  performing  most  effectively 
one  function. 

This  function  is  primarily  one  of  reaction,  a  reaction  which 
includes  two  factors,  excitability  and  conductivity.  It  is  very 
doubtful  whether  nerve  cells  possess  any  automatic  function  what- 
soever. Even  after  large  doses  of  strychnine  have  been  adminis- 
tered in  the  absence  of  all  afferent  impulses,  a  condition,  for  in- 
stance, which  exists  after  the  section  of  all  the  posterior  nerve 
roots,  a  frog  will  lie  absolutely  motionless. 

Such  serious  changes  in  respiration  are  induced  after  cutting 
off  all  afferent  impulses  that  it  is  possible  that  the  demarcation 
currents,  due  to  the  trauma  of  the  cut  nerves  may  account  for  the 
incomplete  and  deficient  respiration  remaining  after  such  an 
experiment. 

174 


THE  NERVOUS  SYSTEM 


TROPHIC   FUNCTIONS   OF   THE    CORD 


We  have  thus  far  considered  only  the  motor  and  sensory  func- 
tions of  the  spinal  cord.  The  spinal  cord  also  exercises  trophic 
functions  upon  both  the  muscles  and  the  skin.  Wlien  its  connec- 
tions with  the  muscles  are  severed,  the  muscles  concerned  atrophy. 
When  the  skin  is  separated  by  division  of  the  posterior  nerve  roots 
it  also  shows  nutritional  changes.  The  skin  becomes  scaly,  glossy, 
and  the  hair  and  nails  show  changes.  When  certain  sensory  nerves 
become  inflamed  peculiar  eruptions  appear.  One  very  characteris- 
tic one  is  known  in  popular  language  as  "shingles."  The  paths 
exerting  trophic  functions  only  become  active  in  post-fetal  life. 
During  intrauterine  life,  even  in  complete  absence  of  the  nervous 
system,  the  muscles  develop  normally. 


176 


Ill 
THE   BRAIN 

Development  of  the  Brain  —  Phylo genetically  the  brain  is 
changed  anterior  segments  of  tlie  cerebrospinal  axis  having  devel- 
oped by  alterations  of  nervous  tissue  similar  in  every  way  to  the 
separate  segments  of  which  the  spinal  cord  in  mainma^s  is  composed 
and  of  which  the  more  definitely  segmental  nervous  system  of  the 
lower  animals  is  formed.  The  alterations  are  due  to  the  addition 
of  new  nerve  tracts  and  new  nerve  centers. 

The  new  nerve  tracts  connect  the  different  portions  of  the  brain 
and  the  brain  with  the  different  segments  of  the  spinal  cord.  The 
new  nerve  centers  serve  as  relay  stations  to  the  tracts  connected 
with  them,  making  possible  a  modification  of  the  afferent  impulses 
reaching  them,  by  passing  them  on  as  efferent  impulses  —  altered 
as  to  their  destination  or  strength  by  a  partial  switching  or  by  other 
impulses  also  reaching  these  centers  from  other  portions  of  the 
nervous  system  —  upon  other  afferent  tracts  to  these  same  centers. 

The  Three  Primary  Cerebral  Vesicles  —  After  the  primary 
neural  groove  has  been  transformed  into  a  tube  at  the  head  end, 
three  cavities  become  constricted  off  in  such  a  manner  as  to  par- 
tially separate  them.  These  three  cavities  are  the  three  primary 
cerebral  vesicles,  and  it  is  from  them  that  the  three  main  divisions 
of  the  adult  brain  develop. 

From  the  anterior  vesicle  develops  the  forebrain  or  the  prosen- 
cephalon. It  may  be  divided  into  the  thalamencephalon,  including 
the  subsequent  cerebral  hemispheres,  the  lateral  ventricles,  the 
retina  and  the  olfactory  lobes,  and  the  diencephalon  which  includes 
the  third  ventricle  and  the  optic  thalami.     (Figs.  76-77.) 

From  the  middle  cerehral  vesicle,  or  the  mesencephalon,  develops 
the  corpora  quadrigemina  and  the  iter  of  Sylvius.  From  the  hind- 
hrain,  the  rhombencephalon,  develops  the  cerebellum,  the  pons  and 
the  upper  half  of  the  fourth  ventricle,  together  constituting  a  sub- 

178 


THE  NERVOUS  SYSTEM 


division  known  as  the  myelencephalon,  and  the  lower  half  of  the 
fourth  ventricle  known  as  the  metencephalon. 

The  retina  of  the  eye  is  developed  from  two  lateral,  stalk-like 
protrusions  from  the  sides  of  the  primary  anterior  cerebral  vesicle. 


Corpora  quadrigemina. 


Cerebellum 


Mesencephalon. 


Pineal  body. 


Pons 
Tarolil. 

Crura  cerebri.  Optic  tbalamus.    |     Pituitary  body.  Foramen  of  Monro. 
Thalamencephalon. 

Fig.  76. — Diagrammatic  sagittal  section  of  a  vertebrate  brain.     (Morris.) 
4,  fourth  ventricle;  s,  cerebral  .aqueduct;  3,  third  ventricle. 

Each  cerehral  hemisphere  also  develops  by  a  bud-like  expansion  of 
the  anterior  extremity  of  the  anterior  cerebral  vesicle.  The  bud 
contains  a  cavity  which  permanently  retains  its  connection  with  the 
original  cavity  of  the  anterior  cerebral  vesicle.    The  growth  of  these 

Epencephalon.        Optic  thalamus. 


Mesencephalon 


Foramen  of  Monro. 


Fig.  77. — Diagrammatic  horizontal  section  of  a  vertebrate  brain. 
4,  fourth  ventricle;  3,  third  ventricle. 


Corpus 
striatum. 


(Morris.) 


buds  is  so  excessive  that  they  completely  cover  the  sides  and  dorsum 
of  the  rest  of  the  brain. 

The  original  cavity  of  the  buds  becomes  the  lateral  ventricle  and 
its  permanent  connection  with  the  cavity  of  the  anterior  cerebral 
vesicle  constitutes  what  afterwards  becomes  the  foramen  of  Monro. 

180 


THE  NERVOUS  SYSTEM 

A  comparison  of  a  schematic  representation  of  the  primary  cerebral 
vesicles  and  the  adult  brain  will  make  these  facts  evident,  and  will 
clearly  establish  the  relative  positions  of  the  various  portions  of  the 
adult  brain. 

Beginning  at  the  transition  between  the  spinal  cord  and  the 
brain  and  passing  from  below  upwards,  the  central  canal  of  the 
spinal  column  opens  out  into  the  fourth  ventricle  of  the  brain.  In- 
cluding its  pontine  portion  the  latter  measures  nearly  two  inches  in 
length  and  about  three-quarters  of  an  inch  in  breadth  at  its  widest 
portion.  Posterior  to  the  medulla  and  forming  a  large  portion  of 
the  roof  of  the  fourth  ventricle  is  the  cerebellum. 

The  cerebellum  forms  a  large  and  separate  division  of  the  human 
brain.  It  measures  about  four  inches  by  two  by  one  and  a  half. 
The  most  prominent  structures  forming  the  lateral  'boundaries  of 
the  fourth  ventricle  are  the  superior,  middle  and  inferior  peduncles 
of  the  cerebellum.  These  are  thick  bundles  of  nerve  fibers  by  which 
the  cerebellum  is  connected  with  the  mid-brain,  the  medulla  and  the 
spinal  cord  respectively. 

The  Fourth  Ventricle  —  The  floor  of  the  fourth  ventricle  con- 
sists of  gray  matter,  which,  in  this  portion  of  the  brain,  represents 
the  gray  matter  of  the  spinal  cord  displaced  posteriorly  by  the 
opening  of  the  central  canal  of  the  latter. 

It  is  diamond-shaped  and  divided  at  its  middle  by  transversely 
running  strands  of  nerve  fibers,  the  strice  acusticcB,  into  an  upper 
pontine  and  a  lower  bulbar  portion.  On  the  floor  of  the  bulbar 
portion  is  a  triangular  depression,  the  ala  cdnerea,  separating  a 
lateral  triangular  prominence,  the  tuierculum  acusticum,  from  a 


median  prominence,  the  / 
The  nucleus  of  the  jm 


trigonum  hypoglossi.     (Fig.  78.) 


leumogastric' nerve  forms  the  gray  matter 
of  the  ala  cinerea.  External  to  it  is  the  nucleus  of  the  eighth  nerve.  ■ 
It  overlies  the  position  of  the  more  deeply  placed  Deiters'  nucleus, 
and  extends  up  under  the  striae  acusticce  into  the  floor  of  the  pon- 
tine portion  of  the  fourth  ventricle.  In  this  region  it  is  separated 
by  a  shallow  depression  from  a  more  medially  placed  elongated 
prominence,  the  eminentia  teres.  The  eminentia  teres  is  formed  by 
the  gray  matter  of  the  nucleus  of  the  sixth  nerve.  It  corresponds 
in  its  position  above  the  strige  acusticse  to  the  trigonum  hypoglossi 
below,  and  its  gray  matter  is  the  direct  continuation  of  the  gray 
matter  of  the  latter. 

182 


THE  NERVOUS  SYSTEM 


184 


THE  NERVOUS  SYSTEM 

The  Iter  of  Sylvius  —  Passing  further  upwards  in  the  exam- 
ination of  the  brain,  the  cavity  of  the  fourth  ventricle  becomes 
again  contracted  into  a  narrow  canal,  the  iter  of  Sylvius  or  the 
Sylvian  aqueduct,  which  runs  between  it  and  the  third  ventricle. 
It  is  rather  more  than  half  an  inch  long.  Like  the  central  canal  of 
the  spinal  cord  it  is  surrounded  by  gray  matter.  The  gray  matter 
of  its  floor  gives  rise  to  the  fourth  and  third  nerves. 

Four  large  nuclei,  two  upon  each  side  of  the  middle  line,  cover 
its  roof.  These  are  called  the  superior  and  inferior  corpora  quad- 
rigemina.  Each  forms  a  prominent  rounded  eminence  upon  the  roof 
of  the  Sylvian  aqueduct.  The  superior  is  intimately  related  with  a 
smaller  cylindrical  eminence  passing  in  an  external  direction  from 
it.  It  is  called  the  external  geniculate  body  and  receives,  together 
with  the  superior  corpora  quadrigemina,  a  large  number  of  the 
fibers  of  the  optic  nerve.  A  similar  cylindrical  eminence  passes 
outward  from  the  inferior  corpora  quadrigemina.  It  is  called  the 
internal  geniculate  body,  and  receives  with  the  inferior  corpora 
quadrigemina  fibers  from  tracts  originating  in  connection  with  the 
nucleus  of  the  auditory  nerve,  situated  below  the  medulla. 

The  Third- Ventricle  —  At  its  upper  extremity  the  iter  of  Syl- 
vius enters  the  third  ventricle.  This  is  a  narrow,  cleft-like  cavity, 
contained  between  two  large  nuclei  of  gray  matter  called  the  optic 
thalami. 

The  optic  thalami  form  the  most  important  and  last  subrelay 
station  for  many  tracts  between  the  cerebrum  and  lower  portions 
of  the  brain  or  spinal  cord. 

The  third  ventricle  is  roofed  in  by  the  concave  lower  surface  of 
the  corpus  callosum,  a  large  mass  of  nerve  fibers  which  collected  in 
an  elongated,  flattened  bundle  connects  the  two  cerebral  hemi- 
spheres. It  is  curved  in  such  a  manner  to  be  convex  above  and 
concave  below. 

The  floor  of  the  third  ventricle  is  formed  of  the  following 
structures  beginning  at  the  front:  The  anterior  perforated  space, 
a  flat  plane  of  gray  matter  which,  with  the  infundibulum,  forms  a 
funnel-like  cavity,  leading  down  to  the  stalk  of  the  pituitary  gland, 
a  pea-sized  structure  situated  below  and  between  the  two. 

Behind  the  infundibulum  is  another  flattened  plane,  the  tuber 
cinereum.    More  posterior  are  two  knob-like  structures,  one  on  each 

186 


THE  NERVOUS  SYSTEM 

side  of  the  middle  line,  called  the  corpora  mammillaria  or  corpora 
albicans. 
.    Between  these  and  the  anterior  opening  of  the  Sylvian  aque- 


Fig.  79. — Under-surface   of  a  simply  convoluted  European  brain.     (Quain.) 
Sulci — orh.,  orbital  (sagittal  rami);  o.tr.,  transverse  orbital;  oZ/.,  olfactory; 
ii,  U-,  ta,  first,  second,  and  third  temporal;  coll.,  collateral  (fourth  temporal); 
calc,  calcarine. 

Gyri — R,  gyrus  rectus;  Ti,  T3,  Ti,  T&,  first,  third,  fourth,  and  fifth  tem- 
poral ;   H,  hippocampal ;  s.  r.  a.,  caput  gyri  hippocampi ;   unc,  uncus. 

ch.,  chiasma;  s.p.a.,  substantia  perforata  antica;  t.c,  tuber  cinereum;  m, 
corpora  mammillaria,  accidentally  separated  from  one  another  in  the  prepara- 
tion; cr.,  crusta;  tm,  tegmentum;  spl.,  splenium  of  callosum. 

duet,  or  iter  of  Sylvius,  is  another  inclined,  flattened  plane  of  gray 
matter,  the  posterior  perforated  space.  Immediately  above  the  an- 
terior opening  of  the  iter  _of  S^vius  is  the  posterior  commissure, 
consisting  of  a  band  of  white  fibers  running  across  the  two  sides  of 

188 


THE  NERVOUS  SYSTEM 

the  brain  in  this  situation  and  composed  of  commissural  fibers  con- 
necting the  posterior  termination  of  the  visual  tracts.  The  extrem- 
ities of  the  commissure  are  in  close  relation  to  the  superior  corpora 
quadrigemina. 

Above  this  commissure  are  the  two  stalks  of  the  pineal  gland, 
which  rests  upon  a  flattened  triangular  surface  in  front  of  and 


Body   of  corpus   callosum 
Intermediate   mass. 
Fornix  ,    1 
Septum    pellucidum.        | 
Marginal    gv  rns   ,       f  „-^l    ' 
of    corpu'=!    callosum   , 
Cingulate  fissure,    x-' 


Tela    ctioroirlea    ventriculi    tertii. 
Cingulate   g^  rus. 

IOallosal    fissure 
I  Siilenuini   of   corjius  callosum. 
,  Paratenlial    lobule. 
*^'.H.     (  ivhinil    fissure. 


Subjiarietal    fissure. 
Precuneate   lobule 
Parieto-occip. 

I     fissure 
~4     iCalcarine 
'i         fissure. 
1      Cuueate 
""k    I    lobule 


Lamina   terminally 

Optic  recess. 

Optic  nerve 

Optic    commissure. • 

Hypophysis. 

Anterior    commissure. 
Foramen   of  Monro 

Third   nerve  f 
Corpus  mammlllare 
Third  ventricle. 
Cerebral   peduncle. 
Pons 
Suprapineal    recess 
Pineal  body 
Cerebral    aqueduct. 


Cerebellum. 
Medulla   oblongata. 
Fourth    ventricle. 
Superior  medullary  velum. 
Corpora   quadrigemina. 


Fig.  80. — Median  section  of  an  adult  brain.     (Quain.) 


between  the  two  superior  corpora  quadrigemina.     This  surface  is 
called  the  trigonum  hal)enulcB. 

Two  other  commissures  cross  the  third  ventricle,  the  middle  and 
anterior  commissure.  The  former  connects  the  two  optic  thalami, 
and  the  latter  is  situated  at  the  extreme  anterior  end  of  the  third 
ventricle  at  the  upper  extremity  of  the  anterior  perforated  space, 
and  is  in  relation  with  it.  It  contains  commissural  fibers  of  the 
olfactory  system.  One  more  bilateral  band  of  commissural  fibers, 
the  pillars  of  the  fornix  and  the  fornix  itself,  appears  in  the  third 

190 


THE  NERVOUS  SYSTEM 

ventricle.  They  run  in  an  anteroposterior  direction.  They  emerge 
from  the  corpora  albicans,  run  forward  to  curve  in  front  of  the 
foramen  of  Monro,  and  then,  reaching  the  roof  of  the  third  ven- 
tricle, they  run  backwards  upon  the  under  surface  of  the  corpus 
callosum,  diverging  as  they  pass  backwards  so  that  ultimately  they 
acquire  a  position  a  little  external  to  the  third  ventricle,  appearing 
by  their  external  edge  in  the  cavity  of  the  lateral  ventricle  upon 
the  upper  and  posterior  surface  of  the  optic  thalami.  In  this  situa- 
tion on  the  side  of  the  lateral  ventricle  they  are  overlapped  by  a 
vascular  fold  of  the  ependyma  or  remnants  of  the  layer  of  epithe- 
lium which  originally  forms  the  roof  of  the  third  ventricle,  before 
the  latter  with  its  ependymal  roof  is  covered  over  by  the  back- 
wardly  growing  hemispheres.  The  ependyma  in  this  manner  be- 
comes enclosed  between  the  fore-  and  mid-brain  and  to  some  extent 
inverted  laterally  into  the  cavity  of  the  lateral  ventricle  by  its  rich 
supply  of  blood  vessels.  It  is  appropriately  named  in  this  situation 
the  velum  interpositum. 


THE    CEREBRAL    HEMISPHERES 

Their  Development  —  The  cerebral  hemispheres  are  formed  by 
an  enormous  growth,  at  first  forwards  then  upwards  and  finally 
backwards,  of  the  anterior  extremity  of  the  anterior  cerebral  ves- 
icles. The  optic  thalami  develop  from  the  thickenings  of  the  lateral 
walls  of  the  anterior  cerebral  vesicle  and,  therefore,  belong  essen- 
tially to  the  third  ventricle. 

The  Lateral  Ventricles  —  Inasmuch,  however,  as.  the  cerebral 
hemispheres  grow  from  the  anterior  end  of  the  anterior  cerebral 
vesicle,  preserving  within  them  a  continuation  of  the  cavity  of  the 
anterior  cerebral  vesicle,  they  may  be  appropriately  viewed  as  rep- 
resenting a  pre-cerehral  vesicle,  developed  in  front  of  the  anterior 
cerebral  vesicle.  This  so-called  pre-cerebral  vesicle  is  carried  back 
with  the  backwardly  growing  cerebral  hemispheres,  and  is  pre- 
served in  the  adult  brain  as  the  lateral  ventricles. 

The  Foramen  of  Monro  —  As  the  lateral  ventricle  is  carried 
backward  external  to  the  third  ventricle,  its  connection  with  the 
third  ventricle  is  placed  laterally  on  each  side  in  the  anterior  ex- 
tremity of  the  third  ventricle.  The  passage  of  connection  is  called 
the  foramen  of  Monro. 

192 


THE  NERVOUS  SYSTEM 


194 


THE  NERVOUS  SYSTEM 

The  Body  —  The  lateral  ventricle  of  the  brain  possesses  a  body 
and  three  horns.     (Figs.  82  and  83.) 

The  body  is  roofed  over  by  the  corpus  callosum.  Its  inner  wall 
is  bounded  by  the  fornix,  overlapped  from  below  by  the  edge  of  the 


Fig.  82. — View  of  the  lateral  ventricle  from  above.  Natural  size.  (Quain.) 
The  preparation  was  made  with  the  brain  in  situ  (hardened).  The  skull 
cap  and  membranes  having  been  removed,  the  brain  was  sliced  down  to  the 
level  of  the  corpus  callosum.  The  left  lateral  ventricle  was  then  opened"  by 
cutting  away  its  roof,  and  the  island  exposed  by  slicing  away  the  opercula. 
The  drawing  is  made  from  a  photograph. 

I.R.,  insula  Reilii  (the  line  points  to  the  middle  of  the  three  gyri  breves); 
S.C.,  sulcus  centralis  insulse;  g.l.,  gyrus  longus  insulte;  c.c,  corpus  callosum; 
n.L.,  nerves  of  Lancisi;  str.t.,  stria  tecta;  f.mi.,  forceps  minor;  j.ma.,  forceps 
major;  c.a.,  cornu  anterius  of  ventricle;  c. p.,  cornu  posterius;  c.i.,  entrance 
to  cornu  inferius;  j.M.,  foramen  Monroi;  s.M.,  sulcus  leading  backwards 
to  the  foramen  Monroi;  c.slr.,  nucleus  caudatus  of  corpus  striatum;  th.opt., 
thalamus,  anterior  tubercle;  pl.ch.,  plexus  choroides;  /.,  fornix;  /',  its  column; 
h.,  posterior  end  of  hippocampus;    tri.,  trigonum  ventriculi;   calcar,  calcar 

196 


THE  NERVOUS  SYSTEM 

velum  interpositum,  called  here  the  choroid  plexus,  because  of  the 
vascular  folds  present  in  its  edge.  Its  floor,  which  curves  upward 
externally  to  meet  the  roof,  is  formed  from  within  outward  by  the 


Fig.  83.— View  from  above  and  the  side  of  the  whole  left  lateral  ventricle. 
Natural  size.     (Quain.) 

This  is  a  further  dissection  of  the  preparation  shown  in  Fig.  82.  The 
insula  has  been  sliced  away  and  the  inferior  cornu,  c.i.,  exposed.  Within 
this  are  seen  the  following  parts:  fi.,  fimbria,  continued  from  the  fornix;  h., 
the  hippocampus;  coll.,  the  eminentia  coUateralis.  The  other  lettering  as  in 
Fig.  82. 


upper  surface  of  the  optic  thalamus,  the  tcenia  semicircularis,  a 
band  of  white  fibers  extending  from  the  region  of  the  septum  luci- 
dum  in  front  backward  and  outwards  along  the  external  superior 
border  of  the  optic  thalamus,  between  it  and  a  large  elongated 

198 


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nucleus  of  gray  matter  immediately  external  to  it  and  called  the 
caudate  nucleus. 

The  Caudate  Nucleus  —  The  caudate  nucleus  is  a  mass  of  gray 
matter  which  really  develops  in  the  external,  downwardly  curving 
fibers  of  the  corpus  callosum.  It  follows,  therefore,  the  general 
shape  of  the  curve  of  the  concave  lower  surface  of  this  body  and, 
as  well,  the  curve  of  optic  thalami,  from  the  outer  border  of  which 
it  lies  separated  by  the  tsenia  semicircularis. 

From  within  outwards  the  optic  thalami,  the  tasnia  semicircu- 
laris, and  caudate  nucleus  form  the  floor  of  the  body  of  the  lateral 
ventricle  and  the  roof  of  its  inferior  horns. 

The  Anterior  Horns  —  The  anterior  horns  of  the  two  lateral 
ventricles  of  the  brain,  arching  around  the  anterior  extremity  of 
the  optic  thalami,  are  separated  from  each  other  by  the  septum 
lucidum,  which  contains  the  fifth  ventricle. 

The  Posterior  and  Inferior  Horns  —  Only  the  space  common  to 
both  the  inferior  and  posterior  horns  bounds  the  posterior  extrem- 
ity of  the  optic  thalami.  The  floor  of  this  common  region  is  formed 
by  a  rather  large,  discoid  eminence  called  the  trigonum  ventriculi. 
Beginning  at  an  area  anterior  to  this  eminence  and  therefore  be- 
tween it  and  the  posterior  extremity  of  the  optic  thalamus  and 
extending  to  the  tip  of  the  inferior  horn  along  its  inner  wall,  is  an 
elongated,  rounded  eminence  called  the  hippocampus  major.  It 
ends  anteriorly  in  a  club-like  extremity  resembling  an  animal's 
paw.  Behind  the  posterior  internal  aspect  of  the  trigonum  ven- 
triculi and,  therefore,  forming  the  internal  wall  of  the  posterior 
horn,  is  another  elongated,  rounded  eminence,  the  hippocampus 
minor.  Another  elongated  fold  or  ridge  appearing  in  the  inner 
wall  of  the  posterior  horn,  is  the  calcar  avis.  It  corresponds  to  an 
important  fissure  on  the  internal  surface  of  the  brain.  Above  it  in 
the  angle  of  the  inner  wall  and  roof  of  the  posterior  horn  is  a  fold 
caused  by  the  fibers  of  the  corpus  callosum,  running  to  the  occipital 
lobe  of  the  brain.    It  is  called  the  forceps  major. 

The  Hemispheres  —  The  external  surface  of  the  brain  presents 
certain  important  fissures  separating  convolutions  identified  with 
various  nervous  activities. 

The  Sylvian  Fissure  —  Upon  the  external  surface  is  the  Sylvian 
fissure.  A  deep  fissure  running  horizontally  backwards  from  a 
position  corresponding  to  the  posterior  border  of  the  lesser  wing  of 

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Great  longitudinal  fissure  of  the  cerebrum — Fissure 
longitudlnalis    cerebri. 

Frontal  pole — Polus  frontalis.  , 


Olfactory  sulcus — Sulcus  olfactorius.  \ 
Orbital  sulci — Sulci  orbitales.  , 


Orbital  gyri. 


Temporal    pole  —  Polus 
temporalis. 


Trigonum  olfactorium. 


Optic  commissure 
or  chiasma  — 
Ohiasma  opticum. 

Uncus  or  hook  of 
the  hippocampal 
gyrus. 

Entrance  to  the 
choroidal  fissure. 


Collateral  fissure 
— Fissura  col- 
lateralis. 


Olfactory  bulb — Bulbus  olfactorius. 

Olfactory  tract — Tractus  olfactorius. 

Gyrus  rectus,- or  straight  gyrus. 

Root  of  the  olfactory  tract,  inm 

or  mesial,  middle  or  gray  an 

outer    or    lateral    root — Strli 

olfactorise,      medialls,      Intel 

media  lateralis. 

Anterior  perforated  spac 

— Substantia     perforat 

anterior. 

.•  Limen  insulae,  or  thresl 

old    of    the    island. 

Fissure      of      Sylvius- 

Pissura   cerebri     la 

eralis    (Sylvii). 

Nucleus  amygdala 
or  amygdaloid  n\ 
cleus. 

Cerebral  peduncle  ( 
crus  c  e  r  e  b  r 
(crusta)  —  Pedui 
cuius  c  e  r  e  b  r 
(based  peduncull' 

Posterior  perforatti 
space  or  fossa 
Tarlnl — Substantii 
perforata  posterloil 


Aqueduct  of  Sylvius — 

AquJEductus  cerebri  (Sylvii) 
Quadrigeminal    lamina — Lamina 
quadrigemina. 
Splenium  of  the  corpus  callosum — Splenium 
corporis    callosi. 
Hippocampal  gyrus. 


Substantia  nigra. 

\  "» V         ft,        y'        ^A.  >      /        •^XX       I  I    \      V  \       I  K  I      /   ^-Jlt 

Third  (or  inferior) 
temporal  sulcus — 
Sulcus  temporalis 
inferior. 

Third    temporal   gyrus. ' 
,      Isthmus  of  the  gyrus  for- 
nicatus  —  Isthmus     gyri 
fornicata. 

Fourth  temporal  gyrus 

Gyrus  fornicatus — Gyrus  fomicatus. 
Occipital  pole — Pole  occipitalis.    Fifth  temporal  gyrus. 

Great    longitudinal    fissure    of    the    cerebrum — Fissure  longitudinalis    cerebri 

Fig.  94. — The  inferior  or  basal  surface  of  the  cerebrum,    facies   basalis    cerebri;    the   whoL 

extent  of  this  surface  is  visible,  the  medulla   oblongata,   pons   varolii,   and   cerebellui 

(i.e.,  the  rhombencephalon)    having  been  removed  by  a  transverse  section  through  th 

mid-brain.     Convolutions  and  furrows  of  the   hemispheres,   gyri    et   sulci   cerebri.     Th' 

frontal,    temporal,    and    occipital    poles    of  the  hemispheres. 

The  anterior  extremity  of  the  left  temporal  lobe  has  been  cut  away,  the  optic  coir 

missure    or   chiasma   has   been   cut   through   in  the  median  plane,  and  its  left  half  has  bee: 

removed.     The   anterior   perforated  space    has   thus   been   fully   exposed   on   the   left   side 

and  its  relations  to  the  threshold  of  the  island,    limen    insula?,    and    to    the    parts    of   th 

rhinencephalon   situate    on   the    mesial   surface   of  the  hemisphere,  have  been  made  man 

fest.     The  olfactory  tract,  tractus  olfactorius,  has  been  cut  away  on  the  right  side,  in  orde 

to  display  the  olfactory  sulcus.     (Toldt.) 


222 


THE  NERVOUS  SYSTEM 

the  sphenoid  to  terminate  in  a  posterior,  upturned  extremity  in  the 
center  of  the  parietal  lobe.  It  separates  the  frontal  lobes  and  an- 
terior portion  of  the  parietal  lobes  from  the  temporal  lobes. 

The  Fissure  of  Rolando  —  The  Fissure  of  Rolando,  beginning 
at  a  point  corresponding  on  the  external  surface  of  the  skull  to  .55 
of  the  distance  from  the  frontal  prominence  to  the  occipital  tuber- 
cle, it  runs  downwards  and  forwards  at  an  angle  of  671/2  °  until  it 
nearly  reaches  the  fissure  of  Sylvius.  It  separates  the  frontal  from 
the  parietal  lobes. 

Superior  and  Inferior  Precentral  and  Intraparietal  Fissures  — 
Fissures  parallel  to  the  fissure  of  Rolando,  the  superior  and  inferior 
precentral  fissures  in  front,  and  the  intraparietal  fissure  behind, 
separate  the  ascending  frontal  convolution  from  the  rest  of  the 
frontal  lobe  and  the  ascending  parietal  convolution  from  the  rest 
of  the  parietal  lobe.  The  remainder  of  the  external  surface  of  the 
frontal  lobe  is  composed  of  the  superior  middle  and  inferior,  or 
first,  second  and  third  frontal  convolutions. 

Parietal  Lobes  —  The  remainder  of  the  parietal  lobe  is  com- 
posed of  the  superior  parietal  lohe,  contained  between  the  forks  of 
the  upper  extremity  of  the  intraparietal  fissure;  the  supra-marginal 
convolution,  curving  around  the  posterior  upper  extremity  of  the 
fissure  of  Sylvius,  and  the  angular  convolution  which  curves  around 
the  posterior  extremity  of  the  superior  temporal  fissure. 

Superior  Temporal  Fissure  —  The  superior  temporal  fissure 
runs  below  and  parallel  to  the  fissure  of  Sylvius  and  separates  the 
first  or  superior  temporal  convolution  from  the  second  or  middle 
temporal  convolution. 

The  Boundaries  of  the  Occipital  Lobe  —  Posterior  to  the  parie- 
tal and  superior,  middle  and  inferior  temporal  convolutions  is  the 
occipital  lohe.  It  is  separated  from  these  lobes  on  the  external  sur- 
face of  the  hemisphere  by  an  imaginary  line  drawn  from  the  point 
where  the  occipito-parietal  fissure  appears  on  the  external  surface 
of  the  brain  and  the  pre-occipital  notch.  The  last  is  an  indentation 
on  the  brain  produced  by  the  attachment  of  the  anterior  border  of 
the  tentorium  cerebelli.  The  frontal,  parietal,  occipital  and  tem- 
poral lobes  extend  over  upon  the  internal  surface  of  the  brain. 

The  Calloso-marginal  Fissure  —  The  inferior  limit  of  the  fron- 
tal lobe  on  the  internal  surface  of  the  hemisphere  is  founded  by  the 
calloso-marginal  fissure.     This  fissure  is  a  prominent  fissure  run- 

224 


THE  NERVOUS  SYSTEM 


ning  concentric  with  the  corpus  callosum  about  half  way  between 
the  latter  and  the  free  margin  of  the  internal  surface  of  the  hemi- 
sphere. Its  posterior  extremity  turns  upward  to  the  free  margin 
of  the  internal  surface  of  the  hemisphere  in  the  parietal  lobe  to  a 
point  posterior  to  the  fissure  of  Rolando. 

The  Limbic  Lobe  —  The  calloso-marginal  fissure  separates  the 
frontal  lobe  from  the  falciform  or  cingulate  or  limbic  lobe.    All  of 


S.  precentralls  tnesialis 

S.  centralis   (Rolandi). 
Pars  marginalis  s 
cinguli. 
S.   parietalis 
superior. 

R.   parieto-         ^    \i^c,V^ 
occipitalis. 


S.  cinguli. 


S.   corporis  callosi 


S.   rostralis. 
Incisura   temporalis. 


S.  calcarlnus. 

S.  subparietalls. 

S.  collateralis 


Fig. 


S.  collateralis. 
S.  temporalis  inferior. 
Fascia  dentata. 


95. — Left   cerebral   hemisphere   from   the   mesial   aspect.     Natural   size. 

(Quain.) 

The  label  "caput  hippocampi"  has  been  placed  too  far  forwards.    The  caput 
hippocampi  does  not  extend  in  front  of  the  incisura  temporalis. 


these  names  are  given  to  the  convolutions  below  the  calloso-mar- 
ginal fissure.  They  are  concentric  with  the  corpus  callosum  and 
curve  around  its  anterior  and  posterior  extremity.  Below  the  pos- 
terior extremity  of  the  corpus  callosum  it  becomes  connected  by  a 
narrow  constricted  portion  with  an  anterior  second  enlarged  por- 
tion. This  enlarged  portion  ends  anteriorly  in  the  uncus,  which  is 
the  anterior  extremity  of  the  limbic  lobe,  marked  off  by  a  narrow 
fissure,  the  dentate  fissure,  from  the  rest  of  the  limbic  lobe. 

The  Precuneus  —  Between  the  posterior  upturned  end  of  the 

226 


THE  NERVOUS  SYSTEM 

calloso-marginal  fissure  and  another  fissure,  the  subparietal  fissure, 
which  continues  the  general  curve  of  the  calloso-marginal  fissure 
around  corpus  callosum,  is  the  portion  of  the  parietal  lobe  which 
appears  on  the  internal  surface  of  the  hemispheres.  This  portion  of 
the  parietal  lobe  is  called  the  precuneus.  That  portion  of  the 
parietal  lobe  appearing  on  the  internal  surface  of  the  hemispheres 
in  front  of  the  precuneus  is  called  the  lohulus  quadratus. 

The  Occipital  Parietal  Fissure  —  Behind  the  precuneus  is  the 
occipital  parietal  fissure,  which  separates  the  precuneus  from  the 
occipital  lobe. 

Calcarine  Fissure  - —  The  occipital  lobe  is  divided  into  two  parts 
by  a  deep  fissure,  curving  downwards  and  backwards  from  the  mid- 
dle of  the  occipital  parietal  fissure  toward  the  posterior  pole  of  the 
brain.    This  fissure  is  called  the  calcarine  fissure. 

Above  the  calcarine  fissure  the  occipital  lobe  is  called  the  cuneus 
and  below  but  more  anteriorly  the  lohulus  Ungualis. 

Collateral  Fissure  —  Beneath  the  lohulus  lingualis,  separating 
it  and,  more  anteriorly,  the  limbic  lobe  from  the  portion  of  the  tem- 
poral lobe  which  appears  on  the  internal  surface  of  the  hemisphere, 
is  the  collateral  fissure.  It  runs  horizontally  between  the  lobes 
which  it  separates.  The  dentate  fissure,  a  small  fissure  in  the  limbic 
lobe  above  and  parallel  to  the  collateral  fissure  produces  the  promi- 
nence of  the  hippocampus  major  upon  the  inner  wall  of  the  inferior 
corhu  of  the  lateral  ventricle.  The  calcarine  fissure  produces  the 
eminence  of  the  calcar  avis  on  the  inner  wall  of  the  posterior  cornu 
of  the  lateral  ventricle. 

The  Fornix  —  The  bundle  of  fibers  forming  the  fornix  terminate 
posteriorly  in  hippocampus  major  and  eminentia  collateralis  — 
structures  to  be  mentioned  later,  and  appearing  in  the  floor  of  the 
descending  horn  of  the  lateral  ventricle  and  posterior  to  the  optic 
thalamus.  They  are  continued  through  the  synapses  of  the  corpora 
albicans  as  another  bundle,  the  bundle  of  Vicq  d'Azyr,  which  curves 
directly  out  of  the  corpora  albicans  into  the  optic  thalami. 
(Fig.  96.) 

The  Character  of  the  Cortex  —  The  external  walls  bounding  the 
lateral  ventricles  as  a  whole,  i.e.,  the  later  transformation  of  the 
precerebral  vesicle,  become  very  much  thickened  in  all  aspects 
except  the  internal,  in  other  words,  above,  externally,  below,  in 

228 


THE  NERVOUS  SYSTEM 


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o  o  -t: 

O;  .-H 

t;|- 

ll^^i 

0  c  ■ 

o 

O  t-l 

fa 

•< 

CJ 

230 


THE  NERVOUS  SYSTEM 

front  and  behind.  This  thickening,  thrown  into  folds  on  its  outer 
surface,  constitutes  the  cortex  and  white  matter  of  the  cerebrum. 

The  Fifth  Ventricle  —  In  front  of  the  foramen  of  Monro  the 
brain  cortex  becomes  coapted  and  united  in  such  manner  that  it 
incloses  a  hollow  cavity,  which  therefore  at  no  time  was  a  part  of 
the  system  of  original  cerebral  vesicles. 

This  cavity  is  called  the  fifth  ventricle  of  the  brain.  Its  walls, 
which  are  formed  of  thin  layers  of  gray  matter,  are  called  the  sep- 
tum lucidum. 

The  Relation  of  the  Optic  Thalami  to  the  Lateral  Ventricles  — 
The  primarily  posterior  and  later  internal  walls  of  the  lateral  ven- 
tricle inclose  the  optic  thalamus  of  the  corresponding  side  by 
curving  around  the  latter.  The  anterior  horn  curves  around  the 
anterior  rounded  end  of  the  optic  thalamus  and  the  inferior  horn 
curves  around  the  posterior  extremity  of  the  optic  thalamus  and 
so  completely  that  at  the  origin  of  this  horn  its  floor  is  formed  by 
the  optic  thalamus,  while  at  its  extremity  its  roof  is  formed  of  the 
optic  thalamus. 

The  posterior  horn  curves  around  in  an  external  direction  the 
posterior  extremity  of  the  optic  thalamus  largely  in  the  same  hori- 
zontal plane  as  that  of  the  body  of  the  lateral  ventricle. 

THE   INTERNAL    STRUCTURE   OP    THE   BRAIN 

There  are  two  important  differences  between  the  internal  struc- 
ture of  the  cord  and  that  of  the  medulla,  which  represent  changes 
of  development  undergone  by  the  medulla  from  the  manner  in 
which  the  cord  develops. 

The  first  of  these  is  the  displacement  of  the  central  canal  pos- 
teriorly until  it  no  longer  forms  a  canal  but  a  median  groove  upon 
the  floor  of  the  fourth  ventricle.  The  second  change  is  the  cutting 
up  of  the  gray  matter  of  the  anterior  horns  by  fibers  of  the  pyram- 
idal tracts  crossing  the  middle  line  and  decussating  with  each  other 
until,  practically  entirely  crossed,  they  occupy  a  situation  on  each 
side  of  the  middle  line  producing  two  rounded  eminences  upon  the 
anterior  surface  of  the  lower  half  of  the  medulla,  immediately  be- 
neath the  pons. 

As  the  central  canal  of  the  spinal  column  opens  up  into  the 
medulla,  the  gray  matter  of  the  posterior  horns  becomes  displaced 

232 


THE  NERVOUS  SYSTEM 


laterally  and  the  gray  matter,  now  in  part  interspersed  between  the 
fibers  of  the  crossing  pyramidal  tracts,  also  becomes  displaced  to  a 
position  on  each  side  of  the  middle  line  in  the  floor  of  the  fourth 
ventricle.  Hence  it  is  that  the  sensory  nuclei  of  the  cranial  nerves 
always  occupy  a  more  lateral  position  than  the  motor  nuclei.  The 
cranial  nerves  may  be  divided  into  motor  nerves  and  sensory  nerves. 
A  number  of  them  have  both  sensory  and  motor  roots. 


Fig.  97. — Diagrams  illustrating  the  origin  and  relations  of  the  root-fibres  of 

the  cerebral  nerves.     (Quain.) 

A,  efferent  fibres  only;  lateral  view.    B  shows  on  the  left  the  motor  nuclei 

and  efferent  fibres,  except  those  of  the  fourth  nerve,  and  on  the  right  side 

the  afferent  fibres:  surface  view.  .    ■    , 

The  Nuclei  and  Superficial  Origin  of  the  Motor  Cranial  Nerves 

(Figs.  97-100)  — From  below  upwards  the  motor  nerves  are  the 
twelfth,  the  seventh,  the  motor  portion  of  the  sixth,  the  fifth,  the 
fourth  and  the  third.  The  nuclei  of  the  twelfth  and  sixth  nerves  lie 
in  the  gray  matter  of  the  floor  of  the  fourth  ventricle,  close  to  the 
middle  line,  one  below  and  the  other  above  the  striae  acusticae  in  just 
the  position  which  the  displaced  gray  matter,  corresponding  to  the 
anterior  horns  of  the  spinal  column,  should  occupy  as  the  conse- 

234 


THE  NERVOUS  SYSTEM 

quence  of  the  opening  out  process  of  the  central  canal  of  the  spinal 
column.  The  nerve  fibers  arising  from  the  cells  of  these  become 
collected  in  bundles  which  pass  outwards  and  forwards  to  emerge  in 
a  series  of  roots  in  the  groove  between  the  pyramids  and  the  olivary- 
body. 

In  the  same  manner  the  sixth  nerve  emerges  from  the  medulla  at 
the  lower  border  of  the  pons  at  the  upper  end  of  the  same  groove. 

In  direct  line  with  these  nuclei,  close  to  the  iter  of  Sylvius,  is  the 


Nucleus   of   ala  cinerea. 


Nucleus   of   tractus    solitarius. 
r  Medial  nucleus  and  descending  root  of 
T      vestibular  nerve. 

Nucleus  of  fasciculus   cuneatus. 


Nucleus  ambiguus. 
—    Restiform  body. 


Root  fllum  of  vagus  cerebello- 
olivary  fibres. 


Ventral  external  arcuate  fibres 


Fig.  98. — Diagram  showing  the  composition  of  the   lerebellar  portions  of  the 
internal  and  external  arcuate  fibres.     (Morris.) 


column  of  nerve  cells  forming  the  nuclei  of  the  fourth  and  third 
nerves.  The  fibers  of  the  fourth  nerve  become  collected  into  a 
bundle  which  passes  backwards  along  the  outer  side  of  the  nucleus 
until  they  reach  the  upper  limits  of  the  medulla  where  they  decus- 
sate and,  after  the  crossing,  emerge  on  each  side  from  the  groove 
at  the  lower  margin  of  the  inferior  corpora  quadrigemina,  between 
this  latter  and  the  superior  peduncle  of  the  cerebellum.  The  other 
cranial  nerves  possess  motor  and  sensory  roots,  but  the  nuclei  of 
the  motor  roots  always  lie  internal  to  those  of  the  sensory  roots. 
Thus  it  is  that  nucleus  of  the  vagus  or  tenth  nerve,  which  is  partly 
motor  and  partly  sensory,  lies  under  the  ala  cinerea  external  to  the 
position  of  the  origin  of  the  twelfth  nerve.  The  motor  portion  of 
the  tenth  arises  from  a  separate  nucleus,  the  nucleus  anibiguus, 

236 


THE  NERVOUS  SYSTEM 


Nucleus  cf  olfactory  nerve. 


Nucleus    of    oculomotor  nerve.  •' 

Nucleus  of  trochlear  nerve. , 

Nucleus    of    mesenceplialic 

root  of  masticator. 
Chief  motor  nucleus  of 
masticator. 


Nucleus    of    facial. "'' 

Nucleus  of  abducens.'' 

Nucleus    ambiguus     (vagus , 

and      glossopharyngeus ) . 

Nucleus  of  hypoglossus 


Nucleus  of   spinal   accessory  nerve. ; 


\  Pulvinar  of  thalamus. 
Lateral  geniculate  body. 
Nucleus  of  superior  colliculus, 

or  corpus  quadrigeminum. 
Sensory  nucleus  of  trigeminus. 
^  Nucleus  of  vestibular  nerve. 


Ventral  nucleus  of 
cochlear    nerve. 


—  Dorsal  nucleus  of  cochlear  nerve. 


Nucleus     alee     cinerese     (vagus     and 
glossopharyngeus). 

Solitary  tract  (vagus  and 
glossopharyngeus). 

Nucleus  of  spinal  tract  of  trigeminus. 


Fig.   99. — Scheme    showing  the   relative   size   and   position   of  the   nuclei   of 

origin    of    the    motor    and    the    nuclei    of    termination 

of  the  sensory  cranial  nerves.     (Morris.) 


238 


THE  NERVOUS  SYSTEM 


Olfactory  tract. 

Hypophysis. 


Anterior  perforated 
substance. 


Mammillary   bodies 


Optic  nerve. 
Optic  tract. 


- —  Tiilter  cinereum. 


Cerebral  peduncle. 


Semilunar  (Gasserian) 
ganglion. 


Oblique  fasciculus  of 
pons. 


Oculomotor 
nerve   (III). 


—  Lateral    genicu- 
late  body. 
Trochlear      nerve 
(IV). 

w^       Masticator    ner 
""-•      (motor  root 
trigeminus). 
^'^  Trigeminus    (V) 

Abducens    (VI) 


Hypoglossal  nerve   (XII) 


Bracliium  of 

Pons. 
Facial    nerve 
..w-  (VII). 

^%^~~ —  Glosso-palatine  ner? 
(intermediate   pal 
of  facial). 
Cochlear      and 
\  fibular     n  e  r  v  e  i 

\  (acoustic  or  VIII) 

\     Glossopharyngeal 
\      nerve   (IX). 

Vagus  nerve   (X). 

Accessory  nerve   (XI) 
(spinal  accessory). 


Cervical  I. 


Decussation  of  pyramids, 


Pyramid.  / 

/ 


^, Cervical  II. 


Fig.  100. — Semi-diagrammatic  representation  of  the  ventral  aspect  of  the  rhombencephalol 
and  adjacent  portions  of  the  cerebrum.    (Morris.) 


240 


I 


THE  NERVOUS  SYSTEM 

which  lies  internal  to  the  sagittal  plane  of  the  main  nnelens.  The 
fibers  of  the  third  nerve  pass  directly  outward  and  ventral-wards, 
traversing  the  substance  of  the  mid-brain  to  emerge  close  to  the 
middle  line  on  the  ventral  surface  of  the  mid-brain  between  the 
diverging  crura  cerebri. 

The  seventh  nerve  arises  from  a  nucleus  external  and  ventral  to 
and  slightly  below  the  nucleus  of  origin  of  the  sixth  nerve,  deeply 
placed  beneath  the  floor  of  the  upper  half  of  the  fourth  ventricle. 
Its  nucleus  would  seem  at  first  sight  to  be  too  far  laterally  placed 
for  a  motor  nucleus,  but  its  deeper  position  in  the  recticular  forma- 
tion explains  this  apparent  irregularity,  for  it  must  be  remembered 
that  all  the  motor  nuclei  of  the  cranial  nerves  occupied  originally 
the  position  of  the  laterally  placed  anterior  horns  and  in  the  open- 
ing out  process  of  the  central  canal  of  the  spinal  column  they  are 
at  first  displaced  from  a  lateral  position  to  an  internal  one.  The 
sexeath^  nerve  possesses  also  a  sensory  root,  which  maintains  its 
integrity  as  a  separate  bundle  of  fibers  at  the  superficial  origin  of 
the  nerve.  Its  incoming  fibers,  like  other  sensory  nerves,  divide  into 
ascending  and  descending  fibers  which  terminate  around  cells  con- 
tinuing the  column  of  the  ninth  nerve  further  upwards.  The  fibers 
of  the  main  portion  of  the  seventh  nerve  are  motor  and  become  col- 
lected into  a  bundle  which  forms  a  peculiar  curve,  at  first  down- 
wards and  inwards  and  backAvards,  then  directly  upwards  and  then 
downwards  and  outwards  and  forwards  in  a  manner  to  completely 
encircle  the  nucleus  of  the  sixth  nerve.  It  finally  emerges  in  the 
groove  between  the  pons  and  the  medulla  just  anterior  to  the  posi- 
tion of  the  superficial  origin  of  the  eighth  nerve. 

The  Sensory  Nuclei  —  It  must  of  course  be  remembered  that 
the  nuclei  of  the  sensory  nerves  are  not  to  be  viewed  as  nuclei  of 
origin,  as  is  the  case  with  the  nuclei  of  the  motor  nerves. 

The  nuclei  of  the  sensory  nerves  are  collections  of  nerve  cells 
around  which  the  termination  of  the  sensory  fibers  arborize. 
Though  more  deeply  placed,  the  nucleus  of  the  ninth  nerve  simply 
continues  upwards,  the  column  of  cells  of  origin  of  the  vagus 
underlying,  in  the  floor  of  the  fourth  ventricle,  an  area  beginning 
in  the  gray  matter  of  the  ala  cinereum  and  extending  upwards 
external  to  the  trigonum  hypoglossi  to  nearly  the  level  of  the  strife 
acusticae. 

The  fifth  nerve  possesses  a  separate  motor  and  sensory  portion. 

242 


THE  NERVOUS  SYSTEM 

The  position  of  its  nuclei  follows  the  general  rule  of  the  other 
cranial  nerves.  The  motor  nucleus  is  situated  at  a  little  depth 
below  the  uppermost  portions  of  the  pontine  part  of  the  medulla, 
at  its  extreme  lateral  portion. 

This,  however,  is  not  a  very  great  distance  from  the  middle 
line,  inasmuch  as  the  fourth  ventricle  is  quite  narrow  at  this  level. 
The  column  of  cells  of  the  main  portion  of  the  motor  nucleus  is 
continued  brainwards,  forming  a  streak  of  gray  matter  external 
and  ventral  to  the  nuclei  of  the  fourth  and  third  nerve  from 
which  fibers  run  downwards  forming  one  bundle  with  the  fibers  of 
the  main  motor  nucleus.  The  collected  fibers  of  the  motor  portion 
of  the  fifth  nerve  emerge  from  the  lateral  surface  of  the  pons. 

The  incoming  fibers  of  the  sensory  portion  of  the  fifth  nerve 
enter  the  pons  immediately  below  the  motor  root.  They  traverse 
the  substance  of  the  pons  and  divide  into  ascending  and  descend- 
ing bundles.  The  ascending  bundles  pursue  a  shorter  course  and 
terminate  around  cells  forming  a  nucleus  which  lies  near  the 
lateral  margin  of  the  pons,  lateral  to  the  motor  nucleus,  though 
not  extending  much  above  the  level  of  the  upper  limits  of  the 
fourth  ventricle. 

The  descending  fibers  run  downwards  for  a  very  long  distance, 
no  less  than  as  far  as  the  level  of  the  second  cervical  nerve.  This 
descending  root  occupies  a  position  at  first  in  the  lateral  boun- 
daries of  the  pons  in  the  substance  of  the  transversely  running 
fibers  of  this  structure.  In  lower  levels  it  lies  close  to  the  super- 
ficial lateral  surface  of  the  medulla  internal  and  posterior  to  the 
corpus  restiforme  and  crossed  laterally  by  the  fibers  of  the  eighth 
nerve.  Still  lower  it  forms  a  cap  at  the  tubercle  of  Rolando  and 
the  substantia  gelatinosa  of  Rolando,  and  may  be  traced  as  far 
down  as  the  second  cervical  vertebros.  Most  of  its  fibers  terminate 
in  the  chief  sensory  nucleus,  situated  dorsally  to  it  in  the  upper 
level  of  the  pons,  lateral  and  ventral  to  the  position  of  the  motor 
nucleus,  coming  very  close  to  the  lateral  surface  in  an  area  indi- 
cated by  the  angle  formed  by  the  superior  and  middle  peduncles 
of  the  cerebellum. 

The  Eighth  Cranial  Nerve  —  The  only  remaining  cranial  nerve, 
exclusive  of  the  optic  and  olfactory  tracts,  which  are  not  peripheral 
nerves  at  all  but  bundles  of  nerve  fibers  comparable  to  intra- 
cerebral tracts,  is  the  eighth  cranial  nerve.    It  is  proper  to  consider 

244 


THE  NERVOUS  SYSTEM 

this  nerve  in  a  class  by  itself  or  with  the  optic  and  olfactory  nerves 
as  it  is  so  specially  proprioceptive  in  its  character  that  it  stands 
quite  apart  from  the  other  cranial  nerves. 

The  eighth  cranial  nerve  is  composed  of  two  portions,  entirely 
different  in  function.  Both  arise  in  the  sensory  cells  of  the  in- 
ternal ear.  One  bundle  of  fibers  constitutes  the  auditory  division 
of  the  nerve  and  the  other  the  vestibular  division.    Both  divisions, 


nmp. 


Fig.  101. — Transverse  section  at  the  upper  part  of  the  medulla   oblongata. 

(Quain.) 

Vy>  pyramid ;  o,  olivary  nucleus ;  d.  V.,  descending  root  of  the  fifth  nei-ve ; 
VIII,  root  of  the  acoustic  nerve,  formed  of  two  parts,  a  (cochlear)  and  b 
(vestibular),  which  enclose  the  restiform  body,  c.r.;  7i.VIIIp,  dorsal  nucleus 
of  the  vestibular  nerve ;  n.  VIII  ac,  ventral  acoustic  nucleus ;  g,  ganglion-cells 
of  the  acoustic  tubercle  (lateral  acoustic  nucleus) ;  n.  f.  t.,  nucleus  of  the 
funiculus  teres ;  n.  XII,  nucleus  of  the  hypoglossal ;  r,  raphe. 


however,  enter  the  medulla  just  beneath  the  pons  Varolii  as  one 
nerve,  parted  as  they  enter  the  medulla  into  a  dorsal  and  ventral 
division  which  inclose  between  them  the  restiform  body.  (Pig. 
101.)  However,  it  is  only  the  auditory  fibers  which  divide  to  in- 
close the  restiform  body.  All  of  the  vestibular  fibers  pass  meso- 
ventral  to  this  structure.  After  it  has  entered  the  medulla  the  ves- 
tibular division  divides,  like  other  sensory  nerves,  into  an  ascending 
and  descending  portion.    Both  divisions  pass  to  the  cells  underlying 

246 


THE  NERVOUS  SYSTEM 

the  area  in  the  floor  of  the  fourth  ventricle,  termed  the  trigonum 
acusticum. 

The  ascending  division  passes  to  the  upper  portion  and  the 
descending  division  to  the  lower  portion.  From  these  fibers  col- 
laterals join  two  other  important  nuclei  —  the  nuclei  of  Bechterew 
and  Deiters,  placed  internal  and  ventral  to  the  restiform  body. 
Many  fibers  of  the  vestibular  nerve  end  directly  around  the  cells 
of  these  nuclei.     The  fibers  of  the  auditory  division  of  the  eighth 


tub.ac. 


FIBRES  TO  NUCL.LEMNtSCI 
&CORPORA  QUADRIGEMINA 


NERVE-ENDINGS 

IN  ORGAN  OF  CORTI 

Fig.  102. — Plan  of  the  course  of  connections  of  the  fibres  forming  the  cochlear 
root  of  the  auditory  nerve.  (Quain.) 
r.,  restiform  body;  Y,  descending  root  of  the  fifth  nerve;  tub.ac,  tuber- 
culum  acusticum;  n.acc,  accessory  nucleus;  s.o.,  superior  olive;  n.tr.,  nucleus 
of  trapezium ;  n.  VI,  nucleus  of  sixth  nei-ve ;  VI,  issuing  root-fibre  of  sixth 
nerve. 


nerve  divide  to  inclose  the  restiform  body.  The  dorso-laferal 
fibers  end  around  cells  forming  a  prominence,  the  tuberculum  acus- 
ticum, on  the  posterior  surface  of  the  restiform  body,  just  above 
the  trigonum  acusticum  and  in  many  cells  interspersed  among  the 
fibers  of  the  dorsal  division  itself.  The  striaa  acusticae  themselves 
are  composed  of  fibers  originating  as  the  axis  cylinders  of  these 
nerve  cells.  They  pass  internally,  crossing  the  middle  line  and, 
therefore,  the  fibers  of  the  opposite  side.  As  soon  as  they  have 
crossed  to  the  opposite  side  they  dip  down  close  to  the  middle 
line  to  enter  the  deep  portions  of  the  medulla  to  be  continued  to 

248 


THE  NERVOUS  SYSTEM 

the  inferior  corpora  quadrigemina  in  a  manner  to  be  subsequently 
described.     (Fig.  102.) 

The  fibers  of  the  auditory  nerve,  which  pass  meso-ventrally  to 
the  corpus  restiforme,  end  around  cells  to  the  inner  and  ventral 
side  of  this  body,  for  the  most  part  placed  between  the  auditory 
and  vestibular  divisions  of  the  eighth  nerve.  Higher  up  these 
cells  become  continuous  with  the  nuclei  of  the  meso-ventral  divi- 
sion.    From  these  nuclei  fibers  also  arise  which  cross  the  middle 


TO  VERMIS 


TO   HEMISPHERE 


FIBRES    OF 

VESTIBULAR 

ROOT 


NERVE 

ENDINGS 

IN  MACULiC' 

&AMPULL/E 


pJ.b 


^GANGLION   OF 
SCARPA 


Fig.  103. — Plan  of  the  course  and  connections  of  the  fibres  forming  the  ves- 
tibular root  of  the  auditory  nerve.  (Quain.) 
r.,  restiform  body;  Y,  descending  root  of  fifth  nerve;  -p.,  principal  nucleus 
of  vestibular  root ;  d,  fibres  of  descending  vestibular  root ;  n.  d.,  a  cell  of  the 
descending  vestibular  nucleus;  D,  nucleus  of  Deiters;  B,  nucleus  of  Bech- 
terew;  n.t.,  nucleus  tecti  (fastigii)  of  the  cerebellum;  plh.,  posterior  (dorsal) 
longitudinal  bundle. 


line,  deeply  decussating  in  the  medulla  in  a  manner  to  be  later 
described  and  ultimately  reach  the  inferior  corpus  quadrigeminum 
of  the  opposite  side.     (Figs.  102  and  103.) 

We  have  now  considered  the  change  produced  in  the  medulla 
by  the  opening  out  of  the  central  spinal  canal,  and  the  effect  which 
this  change  has  produced  upon  the  location  of  the  nuclei  of  the 
cranial  nerves. 

The  Nuclei  Cuneatus  and  Gracilis  —  It  now  remains  to  con- 

250 


THE  NERVOUS  SYSTEM 

sider  the  new  nuclei  appearing  throughout  the  medulla  and  mid- 
brain and  the  further  course  through  the  medulla  and  mid-brain 
of  the  axis  cylinders  of  these  nuclei,  of  the  nuclei  of  the  afferent 
cranial  nerves  and  of  other  great  sensory  tracts.  The  first  impor- 
tant new  masses  of  gray  matter  met  with  are  the  nuclei  cuneatus 
and  gracilis,  at  the  level  of  the  lower  half  of  the  medulla  oblongata 


Funiculus  gracilis 
Dorsal  median  fissure 


Funiculus  cuneatus 
Nucleus  gracilis. 


Descending  root  of  Vth. 
Bundle  from  funiculus 
cuneatus. 
Substantia  Rolandi. 


Bundle  of  Flechsig. 
Pyramid-tract  bundles. 


Decussation  of  pyramids. 


Caput  cornu  ventralis 


Ventral  median  fissure. 


Pyramid. 


Fig.   104. — Section   across   the  lower  part   of  the   medulla   oblongata  in  the 

middle  of  the  decussation  of  the  pyramids.     Magnified 

about   six  diameters.     (Quain.) 


situated  on  its  dorso-external  aspect,  external  to  the  fourth 
ventricle.  They  receive  around  their  nerve  cells  the  terminal 
arborizations  of  the  fibers  of  the  posterior  columns  of  Goll  and 
Burdach  respectively.     (Figs.  104  to  107.) 

Tubercle  of  Rolando  —  Another  nucleus  of,  gray  matter  ex- 
ternal and  ventral  to  the  nucleus  cuneatus  is  the  tubercle  of 
Rolando.  This  is  not  a  new  mass  of  gray  matter  but  it  will 
make  the  description  clearer  to  mention  it  at  this  place.  The 
tubercle  of  Rolando  is  merely  the  enlarged  upper  extremity  of  the 
gray  substance  of  the  substantia  gelatinosa  of  Rolando  around 

252 


THE  NERVOUS  SYSTEM 

the  posterior  horns.    Around  its  cells  doubtlessly  terminate  many 
fibers  of  the  descending  root  of  the  fifth  nerve. 

Corpus  Restiforme  (Figs.  109-111) — The  tubercle  of  Ro- 
lando appears  to  be  overlapped  at  its  upper  extremity  by  bundles 
of  fibers  {two  bundles  in  particular)  which  join  to  form  the  begin- 
ning of  the  inferior  peduncle  of  the  cerebellum  and  constitute  the 
corpus  restiforme.y'^T'his  body,  therefore,  is  in  the  lateral  aspect 


Funiculus  gracilis. 
Funiculus  cuneatus.   - — ■:.'..- 


-  Dorsal  median  fissure. 


Funiculus  Rolandi. 
Substantia  Rolandi. 


Nucleus  gracilis. 
-  Nucleus  cuneatus. 


—  Central  canal. 


Bundle  of  Flechsig. — 
Lateral  nucleus. 


Decussation   of 
pyramids. 


Caput  cornu  ventralis. 


\- 


\ 
Pyramid 


Ventral  median 
fissure. 


Fig.  105. — Section  across  the  medulla  oblongata  at  the  level  of  the  upper- 
most part  of  the  decussation  of  the  pyramids.     (Quain.) 


of  the  medulla,  just  below  the  pons  Varolii  and  just  above  the 
tubercle  of  Rolando  and  the  termination  of  the  column  of  Burdac-h 
in  the  nucleus  cuneatus. 

Olivary  Nucleus  —  A  third  new  mass  of  gray  matter  appear- 
ing in  the  medulla  is  the  olivary  nucleus.  It  presents  a  "vfavy 
appearance  on  cross  section,  arranged  in  a  curved  manner,  concave 
internally,  and  produces  a  very  decided  prominence  between  the 
prominences  of  the  pyramids  and  the  tubercle  of  Rolando  imme- 
diately below  the  pons  Varolii. 

Superior  Olive  —  The  fourth  new  mass  of  gray  matter  is  the 

254 


THE  NERVOUS  SYSTEM 

superior  olivary  7iucleus,  smaller  and  -situated  above  the  main 
olivary  nucleus,  in  among  the  transversely  coursing  fibers  of  the 
pons  Varolii  itself. 

Formatio  Reticularis  —  The  transversely  running  fibers  of  the 
pons  Varolii  form  a  large  portion  of  the  pontine  portion  of  the 


Gracile  nucleus 


Fasciculus  cuneatus 


Cuneate  nucleus 

Tractus  solitarius 
Tractus       spinalis       of 

trigeminal    nerve. 
Nucleus       of       tractus  ftS  "^ 

spinalis    of    trigemi 

nal  nerve. 
Internal   arcuate   fibre 

Fila.  of  hypoglossal 
nerve. 


External  arcuate  fibres 


Inferior    olivary 
nucleus. 


Medial   accessory   olivary 
nucleus. 

Pyramid 


Central  canal. 


Hypoglossal  nucleus 


Fasciculus 

longitudinalis 

medialis. 
Hypoglossal  nerve. 


Raphe. 

Medial  lemniscus. 


External  arcuate 
fibres. 


Fig.   106. — Transverse  section  through  the  middle   of  the   olivary  region   of 
the   human    medulla    oblongata.      (Cunningham.) 
The  floor  of  the  fourth  ventricle  is  seen,  and  it  will  be  noticed  that  the 
restiform  body  on  each  side  has  now  taken  definite  shape. 


medulla.  They  are  composed  of  a  large  number  of  interlacing 
fibers  passing  between  the  two  hemispheres  of  the  cerebellum. 
A  portion  of  these  fibers  are  the  pyramidal  tracts  on  their  way 
from  the  brain  to  the  spinal  cord.  In  other  words,  the  fibers 
of  the  pyramidal  tracts  plunge  deeply  into  the  pons  Varolii  and 
become  covered  and  broken  up  by  the  transverse  fibers  of  this 
structure  before  they  become  united  again  to  form  the  pyramids 
just  above  their  decussatioii      Nevertheless,  many  of  the  pyram- 

256 


THE  NERVOUS  SYSTEM 

idal  fibers  remain  collected  in  the  pons  in  a  fairly  well-defined 
bundle  near  tbe  anterior  surface  of  the  pons.  More  dorsally 
other  transverse  fibers,  which  at  higher  levels  become  longi- 
tudinal, spring  from  the  nucld  cuneatus  and  gracilis.  Still  other 
transverse  fibers  cross  the  middle  line  from  each  olivary  nucleus 
and  from  each  Deiters'  nucleus.    All  these  fibers,  with  others  origi- 


Fasciculus  cuneatus. 

Vestibular  nucleus. — 

Restiform  body. 

Fasciculus  solltarus.  ■ 

Bundle  of  Plechslg.      — 

Descending  root  of  Vtb.  — 

Substantia  Rolandi    - — 

Part  of  descending 

root  of  Vth.         -. — 

Internal  arcuate  fibres,  -i — 

Fibres  of  Xth._ 
Bundle  of  Gowers , 


Raphe. .__—_; 
Thalamo-ollvary  tract. —— -  — 

Accessory  olivary — 

nucleus. 

Olivary  nucleus." ■ 


Fibres  of  Xllth  nerve 


External  arcuate  fibres. 


Pyramid. 

Arcuate  nucleus. 


Dorsal 

longitudinal 
bundle. 

•  Ventral 

longitudinal 
bundle. 


'Inter-olivary 
fibres. 


Fig.   107. — Section  across  medulla  oblongata  a  little  above  the  level  of  the 
point  of  the  calamus  scriptorius.    Magnified  about  six  diameters.    (Quain.) 


nating  from  scattered  cells  among  the  fibers  themselves,  form  a 
confused  network  dorsal  to  the  main  mass  of  fibers  of  the  pons 
Varolii  and  constitute  what  is  known  as  the  formatio  reticularis. 
The  Cerebellum  —  The  gray  matter  of  the  cerebellum,  with 
its  contained  nuclei,  must  also  be  considered  as  additional  masses 
of  gray  matter  added  to  the  primitive  segmented  cerebrospinal 
axis  of  the  invertebrates.  As  explained,  it  is  connected  by  two 
superior,  two  middle  and  two  inferior  peduncles,  with  respectively 
the  mid-brain,  the  medulla  and  tbe  fourth  ventricle.    The  cerebel- 

258 


THE  NERVOUS  SYSTEM 


bO 


^ 


i         -T3, 


a    2 


-13  O" 


I 


260 


to 


THE  NERVOUS  SYSTEM 


262 


THE  NERVOUS  SYSTEM 


bO 

0 

O 


3 
^ 


60 
1^ 


264 


THE  NERVOUS  SYSTEM 

lum  itself  is  composed  of  two  lateral  hemispheres  and  a  central 
lobe  which  latter  appears  as  rounded  eminences  on  the  superior 
and  inferior  surface  of  the  cerebellum  between  the  lateral  hemi- 
spheres.    These  eminences  are  termed  the  superior  and  inferior 


Fig.  111. — Transverse  section  of  pons  through  the  origin  of  the  auditory  nerve. 
From  a  photograph.  Magnified  about  four*  diameters.  (Quain.) 
v.IV,  fourth  ventricle;  c,  white  matter  of  cerebellar  hemisphere;  c.d., 
corpus  dentatum  cerebelli ;  fl.,  flocculus ;  c.  r.,  corpus  restiforme ;  R,  Roller's 
"ascending"  auditory  bundle  (really  formed  of  descending  fibres  of  vestibular 
nerve);  D,  Deiters'  nucleus;  VIII,  root  of  auditory  nei"ve;  VIII d.,  principal 
nucleus  of  vestibular  division;  VIII  v.,  ventral  nucleus  of  cochlear  nerve; 
n.  tr.,  small-celled  nucleus  traversed  by  fibres  of  the  trapezium;  tr.,  trapezium; 
/.,  main  fillet;  p.l.b.,  posterior  or  dorsal  longitudinal  bundle;  f.r.,  formatio 
reticularis ;  n,  n' ,  n" ,  nuclei  in  formatio  reticularis ;  V.  a.,  so-called  ascending 
root  of  fifth  (really  descending);  s.g.,  substantia  gelatinosa;  s.o.,  upper 
olivary  nucleus ;  VII,  issuing  root  of  facial ;  n.  VII,  nucleus  of  facial ;  VI, 
root-bundles  of  abducens;  py.,  pyramid-bundles;  n. p.,  nuclei  pontis. 


vermis.  (Figs.  120-122.)  The  entire  surface  of  all  lobes  is  com- 
posed of  gray  matter,  thrown  into  folds  for  the  purpose  of  increas- 
ing its  surface. 

Its  Nuclei  —  In  the  center  of  each  lateral  hemisphere  is  placed 

266 


THE  NERVOUS  SYSTEM 


ractus 
spinalis   of 
trigeminal 
nerve. 

Its    nucleus 


Facial  nerve, 
aclal  nucleus, 


aperlor    olive, 


Nucleus    of 

tractus. 
Spinalis    of 

trigeminal 

nerve. 
Vestibular 

nerve. 
Tractus 

spinalis    of 

trigeminal 

nerve. 
Facial  nucleus. 

Facial    nerve. 

Superior    olive. 


Corpus 
trapezoldeum. 


Brachlum  pontls. 


Deep  transverse 
fibres  of  pons. 


Pyramidal  bundles. 
Super&cial  transverse  fibres  of  pons. 

g.  112. — Section  through  the  lower  part  of  the  human  pons  immediately  above  the  medulla 

oblongata.    (Cunningham.) 


268 


THE  NERVOUS  SYSTEM 


J3 
bO 

a 
'3 
d 

3 

u 


O 


270 


60 


THE  NERVOUS  SYSTEM 


Upper  and  fourth  ventricle. 

Mesencephalic   root  of   the 
trigeminal  nerve. 

Medial  longitudinal  __ 
bundle. 


Formatio   reticularis 


Anterior  medullary  velum. 
Gray  matt€fr  on  floor  of 
fourth  ventricle. 
Brichlum 

conjunctivum. 
Lemniscus 
lateralis. 


Commencing 
decussation 
of  brachla 
conjunctiva. 

Lemniscus 
medialis. 


Fig.  114. — Section  through  the  superior  part  of  the  pons  of  the  orang,  above 
the   level    of   the    trigeminal    nuclei.      (Cunningham.) 


272 


THE  NERVOUS  SYSTEM 


Root  bundle  of  IVth 
Ace.  motor  root  of  Vtb. 


Sup.  cerebell.  ped. 


Part  of  lateral  fillet. 
Dorsal  long,  bundle. 

Ventral  iSng.  bundle.— 

t 

f 

Lateral  fillet.  — ^ 

I' 

Decuss.  of  superior  peduncles. L 


—-   Main  fillet. 


Substantia  nigra. 


Central  nucleus. 


Crusta  or  pes  pedunculi 


"^sS^ 


Breaking   up   of   crusta   into  pyramid-  — 
bundles.  ^ 


Fig.  115. — Transverse  section  through  the  uppermost  part  of  the  pons. 

(Quain.) 


274 


THE  NERVOUS  SYSTEM 


,'77..m,IV 


i^i^T 


>■-•,-'     -^^^^.^.z        V'^vV        ■«4.i|  'I  /       (. 


Fig.  116. — Transverse  section  across  the  mid-brain  through  the  posterior  cor- 
pora  quadrigemina.     Magnified   about   3%    diameters. 
From  a  photograph.     (Quain.) 
gr.,   dorsal    quadrigeminal    groove    (sulcus    longitudinalis) ;    c.  q.  p.,    corpus 
quadrigeminum  posterius;  str.L,  stratum  lemnisci;  c.gr.,  central  gray  matter; 
n.  Ill,  IV,  oculomotor  nucleus ;   d.  V,  descending  motor  root  of  fifth  nerve ; 
p.l.b.,   posterior   longitudinal   bundle;    f.r.t.,   formatio   reticularis   tegmenti; 
d.  d',   decussating  fibres  of  tegmentum    (fountain-like   decussations   of   Forel 
and   Meynert) ;    s.c.p.,   decussating   fibres   of  superior   cerebellar   peduncles; 
/,  main  fillet;  /',  lateral  fillet;  pp.,  crusta  pedunculi;  s.n.,  substantia  nigra; 
g.i.p.,  interpeduncular  ganglion;  sy.,  Sylvian  aqueduct. 


276 


THE  NERVOUS  SYSTEM 


Central  gray 
matter. 


Aqueduct, 


Inferior  colliculus. 

Mesencephalic  root  of  trigeminal  nerve. 
Nucleus  of  trochlear  ner^e. 
Brachiuai  inferio'" 

v-s^l^i.^.^^^^^.  Medial  longitudinal  bundle 


Medial  lemniscus. 


Braehlum 
conjunctivum 


Basis  peduncuU. 


Fig.  117. — Transverse  section  through  the  human  mesencephalon  at  the  level 
of  the  inferior  colliculus.     (Cunningham.) 


278 


THE  NERVOUS  SYSTEM 


bO 


280 


THE  NERVOUS  SYSTEM 


Fig.  119. — Section  across  the  mid-brain,  through  the  anterior  corpora 
quadrigemina.  Magnified  about  3%  diameters.  (Quain.) 
Sy.,  aqueductus  Sjdvii;  c.p.,  commissura  posterior;  gl.pL,  corpus  pinealis; 
c.  q.  a.,  gray  matter  of  one  of  the  anterior  corpora  quadrigemina ;  c.  g.  m., 
corpus  geniculatum  mesiale;  e.g.  I.,  corpus  geniculatum  laterale;  tr.opt., 
tractus  opticus;  pp.,  pes  pedunculi;  p. Lb.,  posterior  longitudinal  bundle; 
fi.,  upper  fillet;  r.n.,  red  nucleus;  n.III,  nucleus  of  third  nerve;  ///,  issuing 
fibres  of  third  nerve;  I. p. p.,  locus  perforatus  posticus. 


282 


THE  NERVOUS  SYSTEM 

an  important  nucleus  of  gray  matter,  the  dentate  nucleus.  On 
cross  section  it  appears  as  a  wavy,  curved  line  concentric  with 
the  surface  of  the  hemispheres. 

The  central  lobe  possesses  three  other  nuclei  on  each  side  of 
the  middle  line.  One,  the  nucleus  fastigii,  is  nearest  the  middle 
line  and  immediately  above  the  roof  of  the  fourth  ventricle.  A 
third  nucleus  lies  dorsal  to  this.    It  is  named  the  nucleus  gldhosus. 


Sulcus  prepyramidalls. 
Sulcus  pregracilis. 


Uvula. 

Tonsilla. 

Lobulus  biventralls. 


Sulcus  Intragracills 
Sulcus  postgracilis. 

Sulcus  horlzontalis  magnus. 


Lobulus  pos- 
tero-supeilor. 
Lobulus  semi- 
lunaris inferior. 
Lobulus  gracilis 
posterior. 
Lobulus  gracilis 
anterior. 
Pyramids. 


Fig.  120. — View  of  cerebellum  from  below.     Natural  size.     (Quain.) 


Between  it  and  the  dorsal  border  of  the  dentate  nucleus  is  still 
another  nucleus,  the  nucleus  ernboliformis.     (Fig.  123.) 

The  Destination  of  the  Superior  Peduncles  of  the  Cerebellum 
—  After  decussation  the  majority  of  the  fibers  of  the  superior 
peduncle  of  the  cerebellum  terminate  in  the  red  nucleus:  The 
upper  termination  of  these  fibers  really  forms  a  capsule  to  the  red 
nucleus. 

The  Red  Nucleus  —  The  red  nucleus  is  situated  at  the  top  of 

284 


THE  NERVOUS  SYSTEM 


a 
"3 
a 

o 


ft 


bJO 


286 


THE  NERVOUS  SYSTEM 


288 


THE  NERVOUS  SYSTEM 

the  mid-brain,  beneath  and  ventral  to  the  corpora  quadrigemina, 
and  dorsal  to  the  inner  portion  of  crura  of  that  side.  Lateral  to 
it  and  dorsal  to  the  external  portion  of  the  crus  is  another  collec- 
tion of  gray  cells  termed  the  substantia  nigra.  (Figs.  118  and  119.) 
Substantia  Nigra  —  The  substantia  nigra  is  found  in  sections 
below  the  level  at  which  the  red  nucleus  is  formed.  It  separates 
the  crusta  of  the  cerebrum  from  a  large  mass  of  transversely  and 
longitudinally  running  fibers,  known  as  the  tegmentum  and  con- 


■plex-us 


Fig.  123. — Section  across  the  cerebellum  and  medulla  oblongata  showing  the 
position  of  the  nuclei  in  the  medullary  centre  of  the  cerebellum.  (Quain.) 
n.d.,  nucleus  dentatus  cerebelli;  s,  band  of  fibres  derived  from  restiform 
body,  partly  covering  the  dentate  nucleus;  s.cp-,  commencement  of  su- 
perior cerebellar  peduncle;  com',  com",  commissural  fibres  crossing  in  the 
median  white  matter. 


sisting  largely  of  fibers  making  up  the  superior  peduncles  of  the 
cerebellum. 

The  Tegmentum  —  Like  the  f ormatio  reticularis  the  tegmentum 
consists  of  many  interlocking  fibers,  definite  bundles  of  which 
belong  to  the  superior  cerebellar  peduncles.    It  also  contains  many 

290 


THE  NERVOUS  SYSTEM 

scattered  nerve  cells  which  form  relay  stations  for  some  fibers 
coming  from  higher  and  lower  levels. 

The  New  Tracts  of  White  Fibers  —  The  important  nuclei  of 
the  brain  stem,  the  medulla  and  mid-brain,  and  cerebellum,  have 
now  been  mentioned.  It  remains  to  describe  the  tracts  of  white 
fibers  connecting  them  and  passing  through  them.  It  will  be  con- 
venient to  start  with  the  various  tracts  of  white  matter  found  in 
the  spinal  cord,  though  it  must  always  be  kept  in  mind  that  those 
tracts  which  carry  impulses  in  a  descending  direction  are  being 

Nucleus  of  fasciculus 

cuneatus.  Nucleus  of  Comlnlssural  nucleus  of  ala  cinerea. 

I    fasciculus  gracilis.    ;  Dorsal  external  arcuate  fibres. 


Restiform    t)ody. 


Spinal  tract  of  . 
trigeminus. 


Ventral  external  arcuate 
fibres. 


Fig.   124. — Diagram  showing  the   composition   of  the   cerebellar  portions   of 
the  internal  and  external  arcuate  fibres.     (Morris.) 

tracted  in  a  direction  opposite  to  that  in  which  they  grow  and 
functionate,  and  toward  the  origin  of  the  axis  cylinders  of  which 
they  are  composed. 

Deep  Arcuate  Fibers  —  We  may  start  first  with  the  posterior 
spinal  columns,  the  column  of  Burdach  and  Goll,  carrying  sensa- 
tions of  muscular  sense  —  muscular  tone  and  reflex  coordination, 
which  reach  consciousness.  These  may  be  traced  to  their  endings 
around  the  cells  in  the  nucleus  cuneatus  and  gracilis.  From  these 
nuclei  other  fibers  are  given  off  which  pass  inward  and  ventrally 
through  the  lower  half  of  the  medulla  to  decussate  in  the  middle 
line  with  similar  fibers  of  the  opposite  side.  These  fibers  are  called 
the  deep  arcuate  fibers.  They  turn  upward  after  decussation,  lying 
close  to  the  middle  line  and  dorsal  to  that  portion  of  the  fibers  of 
the  pons  Varolii  which  surrounds  the  pyramids  as  they  pass  up- 

292 


THE  NERVOUS  SYSTEM 


wards.     They  form  a  well-marked  bundle  in  this  situation  called 

the  mesial  fillet.    (Figs.  124-125  and  105  to  119.) 

The  mesial  fillet  may  be  traced  upwards  through  the  mid-brain 

where  it  occupies  a  more  lateral  position.    Above  the  pons  Varolii 

it  leaves  the  middle  line 
beneath  the  superior  pe- 
duncle of  the  cerebellum, 
and  at  higher  levels  is  lat- 
eral to  the  decussation  of 
the  superior  peduncles. 
The  mesial  fillet  termi- 
nates in  the  superior  cor- 
pora quadrigemina,  in  the 
external  geniculate  bodies 
and  in  the  optic  thalami. 
Superficial  Arcuate  Fi- 
bers—  A  second  set  of 
fibers  are  given  off  from 
the  nuclei  cuneatus  and 
gracilis,  passing  externally 
and  ventrically  instead  of 
internally.  These  are  the 
superficial  arcuate  fibers 
which  pass  over  the  tu- 
bercle of  Rolando,  over 
the  upper  portion  of  the 
olivary  prominence,  over 
the  pyramids,  over  the  op- 
posite olive  and  tubercle  of 
Rolando,  to  join  the  cor- 
pus restiforme  of  the  oppo- 
site side.    A  number  of  the 


Fig.  125. — Diagram  of  the  spino-cerebel- 
lar,  bulbo-tegmental,  cerebello-tegmental, 
ponto  -  tegmental,  and  ponto  -  cerebellar 
tracts.     (Quain.) 


axons,  particularly  those  springing  from  a  little  accessory  cuneate 
nucleus  on  the  lateral  surface  of  the  main  nucleus,  join  the  resti- 
form  body  of  the  same  side.  As  the  restiform  body  forms  the 
inferior  peduncle  of  the  cerebellum  the  ultimate  termination  of 
these  fibers  is  to  the  gray  matter  of  this  portion  of  the  cerebellum. 
They  run  directly  to  the  cortex  particularly  of  the  vermis. 
(Fig.  124.) 

294 


THE  NERVOUS  SYSTEM 

The  Termination  of  the  Direct  and  Crossed  Cerebellar  Tracts 

—  Two  more  tracts  in  the  spinal  cord  convey  sensations  of  mus- 
cular tone  and  muscular  coordination.  They  are  the  direct  cere- 
bellar tract  and  the  anterior  cerel)ellar  tract.  The  former  convey 
the  uncrossed  muscular  sensations  which  do  not  reach  conscious- 
ness. Their  axons  originate  in  the  cells  .of  Clark's  column  and 
they  pass  directly  into  the  corpus  restiforme  and  then  to  the  cere- 
bellum. The  antero-lateral  cerebellar  tract  carries  crossed  mus- 
cular sensations  which  do  not  reach  consciousness.  The  fibers  of 
this  tract  travel  upward  through  the  formatio  reticularis  of  the 
medulla  oblongata,  representing  the  only  longitudinal  spinal  fibers 
in  the  upper  part  of  the  pons  after  the  removal  of  direct  cerebellar 
tracts  and  the  posterior  columns,  with  the  exception  of  the  pyram- 
idal tracts.  That  portion  of  this  tract,  the  posterior  portion,  which 
conveys  muscular  sensations,  leaves  the  medulla  by  bending  directly 
dorsally  to  join  the  superior  peduncles  of  the  cerebellum,  passing 
with  them  to  the  cerebellum.     (Figs.  124  and  125.) 

The  Spino-thalamic  Fibers  —  Other  bundled  of  the  antero- 
lateral column,  the  spino-thalamic  fibers,  convey  sensations  of  pain, 
of  heat  and  cold,  and  of  touch  and  pressure.  These  fibers  form 
the  column  of  Gowers  internal  to  the  crossed  cerebellar  tract  and 
a  bundle  anterior  to  it.  The  two  sets  of  fibers  join  the  medial 
fillet  and  end  with  this  bundle  in  the  optic  thalamus.  As  new 
masses  of  gray  matter  than  those  represented  in  the  cord  develop 
within  the  medulla  and  mid-brain,  so  also  new  tracts  of  fibers  are 
found  in  these  portions  of  the  brain.     (Fig.  125.) 

The  Connections  of  the  Olive  —  The  inferior  olivary  nuclei 
are  directly  connected  by  some  fibers  with  the  corpus  restiforme 
and  hence  with  the  cerebellum  of  the  same  side.  Most  of  the 
fibers,  however,  which  are  associated  with  the  olivary  nuclei, 
pass  across  the  middle  line  through  the  opposite  olive  and  into  the 
opposite  corpus  restiforme.  These  fibers  are  axis  cylinders  of  the 
olivary  bodies  —  at  least,  ablation  of  one  cerebellar  hemisphere 
will  cause  atrophy  of  the  opposite  olive.  It  is  possible  that  some 
of  the  olivo-cerebellar  fibers  may  be  efferent  from  the  cerebellum, 
as  some  fibers  originating  in  the  olivary  nucleus  pass  directly 
down  into  the  cord,  and  after  being  joined  with  other  fibers  from 
the  optic  thalamus  help  to  form  the  thalamic  or  olivospinal  tract 
of  Ilelweg.    This  tract  then  is  a  descending  tract,  but  it  has  been 

296 


THE  NERVOUS  SYSTEM 

convenient  to  describe  it  with  the  other  connections  of  the  olivary 
nucleus.     (Fig'.  98.) 

The  Various  Fibers  Constituting  the  Corpus  Restiforme,  or 
Inferior  Peduncle  of  the  Cerebellum  —  Before  describing  other 
descending  tracts,  one  other  important  connection  to  the  restiform 
body  remains  to  be  described.  Some  of  the  fibers  of  the  vestibular 
branch  of  the  eighth  nerve,  which  are  connected  by  collaterals 
with  the  nuclei  of  Bechterew  and  Deiters,  form  a  bundle  known 
as  the  internal  restiform  hody.  The  internal  restiform  body  also 
contains  fibers  from  the  nuclei  of  the  glossopharyngeal  nerve  and 
probably  fibers  running  directly  from  the  nuclei  of  Bechterew  and 
Deiters.  This  bundle  joins  with  the  arcuate  fibers  and  passes  into 
the  corpus  restiforme  and  inferior  peduncle.  The  following 
bundles  of  nerve  fibers,  therefore,  run  to  the  cerebellum. 

1.  Fibers  originating  in  Clark's  columji  of  cells,  homolateral 
and  ascending  in  the  direct  cerebellar  tract. 

2.  Fibers  from  the  dorsal  nuclei  of  the  posterior  columns  of 
the  same  and  opposite  side. 

3.  Internal  and  superficial  arcuate  fibers  from  the  olivary 
bodies. 

4.  From  the  vestibular  nerve,  the  glossopharyngeal  nerve  and 
Deiters  nucleus.  All  these  fibers  run  directly  to  the  cortex  of  the 
cerebellum,  particularly  the  cortex  of  the  vermis. 

The  Middle  Peduncle  of  the  Cerebellum,  or  the  Pons  Varolii 
—  The  cortex  of  cerebellar  hemispheres  receives  most  of  its  af- 
ferent fibers  from  the  middle  peduncle.  The  pons  Varolii  is  largely 
composed  of  fibers  which  are  only  commissural  and  run  from  one 
cerebral  hemisphere  to  the  other.  A  large  number  of  fibers  enter- 
ing the  middle  peduncle  are  axis  cylinders  of  cells  in  the  formatio 
reticularis ;  others  are  efferent  and  end  around  cells  in  the  formatio 
reticularis.  Many  fibers  of  the  crura  cerebri  pass  between  the 
frontal  and  temporal  lobes,  and  the  formatio  reticularis  of  the 
opposite  side.  It  is  therefore  in  the  formatio  reticularis  that  one 
connection  between  the  cerebral  cortex  and  the  cerebellum  is 
effected. 

The  Afferent  Tracts  to  the  Cerebellum  in  the  Superior  Pe- 
duncle —  Two  other  afferent  tracts  enter  the  cerebellum.  They 
have  been  previously  mentioned.  One  ascends  from  the  cord  in 
the  lateral  part  of  the  antero-lateral  column,  conducting  the  crossed 

298 


THE  NERVOUS  SYSTEM 

conscious  muscular  sensations  and  passes  into  the  cerebellum  by 
the  superior  peduncle.  The  second  arises  in  cells  of  the  superior 
corpora  quadrigemina  and  passes  into  the  cerebellum  also  by  the 
superior  peduncles. 

Inasmuch  as  the  superior  corpora  quadrigemina  receive  the 
fibers  of  the  optic  nerve,  this  tract  must  transmit  association  im- 
pulses important  for  muscular  coordination  between  the  sense  of 
vision  and  the  cerebellar  centers,  an  association  much  used  in  many 
muscular  movements,  few  of  which  are  not  guided  by  sense  of 
vision.  So  much  for  the  afferent  tracts  of  the  cerebellum.  The 
efferent  fibers  to  the  cells  of  the  formatio  reticularis,  contained  in 
the  middle  peduncle,  have  been  mentioned. 

The  Efferent  Tracts  from  the  Cerebellum  —  All  efferent  fibers 
from  the  cerebellum  leave  from  the  central  nuclei,  the  nucleus 
dentatum,  fastigii,  globosus  and  emboliformis.  No  efferent  cere- 
bellar fibers  leave  the  cortex.  A  large  mass  of  fibers  leave  the 
nucleus  dentatum  and  pass  by  the  superior  peduncle  to  the  red 
nucleus  and  subthalamic  region  of  opposite  side.  A  certain  number 
of  fibers  pass  also  from  the  central  nuclei  to  the  corpora  quadri- 
gemina of  the  same  side.  No  fibers  pass  directly  to  the  spinal 
cord  but  important  tracts  run  between  the  central  nuclei  and 
the  nucleus  of  Bechterew  and  Deiters.  From  these  nuclei  large 
tracts  run  down  to  the  different  levels  of  the  spinal  cord  in  the 
antero-lateral  column  constituting  the  vestibulo-spinal  column. 
It  is  doubtless  in  part  through  this  tract  that  the  impulses  of 
equilibrium  are  capable  of  affecting  the  motor  apparatus  of  the 
spinal  cord,  passing  by  way  of  the  vestibular  nerve,  fir.st  to  the 
cerebellum  where  they  become  modified  into  impulses  permitting 
finer  muscular  adjustments  by  association  with  other  impulses 
within  this  large  center  of  coordination  where  all  impulses  having 
to  do  with  muscular  contraction  meet. 

The  Trapezium  and  Lateral  Fillet  (see  Figs.  102  and  126)  — 
Two  other  tracts  of  white  matter  through  the  mid-brain  and  medulla 
are  yet  to  be  considered.  One  of  these  connects  the  nuclei  of  the 
auditory  nerve  with  the  inferior  corpora  quadrigemina.  From  both 
divisions  of  the  nuclei  of  the  auditory  nerve,  the  dorsal  and  ventral 
nucleus,  nerve  fibers  pass  internally  to  decussate  with  similar  fibers 
of  the  opposite  side  ^Figs.  105  to  116.) 

This  decussating  tract  is  called  the  trapezium  and  forms  a  defi- 

300 


THE  NERVOUS  SYSTEM 

nite  structure  in  the  medulla.  The  trapezium  is  situated  just 
dorsal  to  the  formatio  reticularis.  It  is  joined  by  nerve  fibers 
from  the  superior  olive  and  by  the  fibers  of  the  strige  acusticae 


Fig.  126. 

A.  Auditory  fibres  passing  by  way  of  the  stria  acustica,  1,  and  the 
trapezium,  2,  and  the  lateral  fillet  to  the  inferior  corpus  quadrigeminum,  3. 

B.  Vestibular  fibres  after  making  connections  through  the  medulla  pass- 
ing to  the  dentate  nucleus,  4. 

C.  Optic  fibres  passing  to  the  superior  corpus  quadrigeminum,  5,  from 
which  fibres  run  to  the  cerebellar  cortex,  6,  and  posterior  longitudinal  bundle, 
7,  which  in  turn  establishes  connections  with  the  III  and  IV  nucleus  and  the 
Vlth  and  the  anterior  horn  cells,  8,  by  means  of  the  antero-lateral  column,  9. 

D.  Afferent  cerebellar  fibres  composed  of  the  posterior  cerebellar  tract,  10, 
to  the  cerebellar  cortex,  6,  and  the  superficial  external  arcuate  fibres,  11,  to 
the  cortex  of  the  vermis.  The  direct  cuneate  cerebellar  fibres,  12,  and  the 
olivo-cerebellar  fibres,  13. 

E.  Efferent  cerebellar  fibres  to  the  red  nucleus,  14,  from  the  dentate 
nucleus,  4. 

302 


THE  iNERVOUS  SYSTEM 

after  these  have  crossed  on  the  floor  of  the  medulla"  and  fibers  from 
the  auditory  nucleus.  All  these  fibers  become  collected  into  a 
bundle  which  passes  upwards  through  the  mid-brain  where  they 
form  the  lateral  fillet.  It  lies  to  the  outer  side  of  the  superior 
cerebellar  peduncle.  It  virtually  passes  around  the  peduncle  on 
its  outer  side  and  in  this  manner  gains  the  inferior  corpora  quad- 
rigemina  in  which  the  fibers  of  the  lateral  fillet  end.  (Figs.  105- 
116.)  The  inferior  corpora  quadrigemina  form  substations  for 
auditory  sensations. 

The  Posterior  Longitudinal  Bundle  —  The  other  white  tract 
through  the  mid-brain  and  pons  is  the  posterior  longitudinal  bundle. 
It  is  an  important  bundle  seen  in  all  sections  through  the  pons  and 
mid-brain,  and  continued  throughout  the  spinal  cord  in  the  antero- 
lateral column  as  the  tract  of  Marie.     (Figs.  126  and  105-116.) 

The  posterior  longitudinal  bundle  is  a  well-defined  tract  run- 
ning near  the  middle  line  just  dorsal  to  the  tegmentum  in  the 
mid-brain,  and  to  the  formatio  reticularis  in  the  medulla  oblongata. 
It  connects  the  nuclei  of  the  various  cranial  nerves  with  each 
other  and  contains,  therefore,  fibers  which  run  in  both  directions. 

Summary  of  the  Various  Substations  —  We  have  now  consid- 
ered the  principal  new  masses  of  gray  matter  which  have  been 
added  to  the  cerebrospinal  axis  in  the  hind  and  middle  brain. 

We  have  also  followed  the  connections  of  these  nuclei,  and  the 
principal  tracts  connecting  these  nuclei  and  carrying  impulses 
from  them  and  from  the  spinal  cord  up  to  them:  they  may  be 
termed  the  terminal  substation  of  impulses,  standing  next  to  the 
cerebrum  in  the  receipt  or  transmission  of  impulses  passing  be- 
tween the  cerebrum  and  the  lower  portions  of  the  nervous  system. 
These  terminal  substations  are  situated  at  different  levels  for 
various  white  tracts  in  the  cerebrospinal  axis.  In  the  ease  of  the 
pyramidal  tracts  the  terminal  substation  between  the  cerebrum 
and  the  spinal  cord  is  in  the  spinal  cord  itself.  In  the  case  of 
other  fibers  also  running  in  the  crura  cerebri  the  terminal  sub- 
station is  in  the  formatio  reticularis.  For  other  tracts  it  is  in  the 
red  nucleus  and  the  corpora  quadrigemina,  while  in  the  case  of 
still  others  the  terminal  station  is  in  the  base  of  the  fore-brain  itself, 
namely  in  the  optic  thalami. 

The  New  Masses  of  Gray  Matter  Belonging  to  the  Fore-Brain 
—  It  now  remains  to  describe  the  new  masses  of  gray  matter  be- 

304 


THE  NERVOUS  SYSTEM 


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THE  NERVOUS  SYSTEM 

longing  to  the  cerebrum  arising  from  what  we  have  termed  the 
preeerebral  vesicles,  and  those  paths  of  connection  between  them 
and  the  so-called  terminal  substations  placed  between  the  cerebrum 
and  the  lower  portions  of  the  cerebrospinal  axis. 


Lateral  ventricle. 
Caudate  nucleus.   | 
Anterior  commissure. 
Lentlform  nucleus 
External  capsule 
Claustrum.  r 


Savum  septi  pellucidl. 
Septum  pellucidum. 
Corpus  callosum. 


Internal  capsule. 


Insula. 


Middle  cerebral  artery. 


Anterior  per- 
forated space. 
I      Optic  tract. 
Internal  carotid  artery.  I    Lamina  terminalis. 

Optic  recess.  Third  nerve. 


Fig.  128. — ^View  from  the  front  of  a  coronal  section  of  an  adult  brain  made 
two  and  a  half  inches  behind  the  frontal  pole  and  nearly  one  inch  behind 
the  temporal  pole  and  about  half  an  inch  posterior  to  the  anterior  end  of 
the  lateral  ventricles.     Five-sixths.     (Quain.) 

The  vallecula  S3dvii  is  seen  on  each  side  external  to  the  optic  commissure; 
on  the  right  side  of  the  brain  the  internal  carotid  artery  is  shown  dividing 
in  this  space  into  the  anterior  and  middle  cerebral  arteries. 


The  majority  of  new  masses  of  gray  matter  of  the  fore-brain 
have  already  been  described.  They  include  the  cerebral  cortex 
itself  and  the  walls  of  the  third  ventricle,  the  structures  appear- 
ing in  the  lateral  ventricles,  the  caudate  nucleus  and  the  optic 
thalami  themselves. 

308 


THE  NERVOUS  SYSTEM 


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THE  NERVOUS  SYSTEM 


THE  NERVOUS  SYSTEM 

The  Internal  Capsule  —  Internal  to  the  optic  thalami  is  the 
third  ventricle,  the  lateral  walls  of  which  are  formed  by  the  optic 
thalami.  A  small  portion  of  the  optic  thalami  appears  in  the 
lateral  ventricle.  Most  of  its  external  surface  is  surrounded  by 
thick,  capsule-like  layer  of  white  fibers  termed  the  internal  capsule, 
the  great  pathway  of  all  afferent  and  efferent  impulses  to  and 
from  the  cerebrum. 

The  internal  capsule  is  formed  of  all  those  nerve  fibers  which 
pass  from  various  portions  of  the  cerebrum  in  the  crura  cerebri, 
and  in  part  of  fibers  emerging  from  the  optic  thalami  to  be  dis- 


Commissura  hippooampi.       Gjrus  clnguU.  [ 


Stria  longitudinalis  medlalis. 

Cavum  septi  pellucidl. 
Septum  pellucidum. 
Ventriculus 
lateralis. 
Crus  foruicis. 


Plexus 

ehorioicleus 
lateralis. 


Tela   chorioiilea. 


Thalamus 
Plexus   chorioideus   vent,   tertii. 


Stria  terminalls. 


Attachment  of  lamina 
chorioidea. 
Thalamus  (free  surface). 
*■  Taenia  thalami. 

Ventriculus  tertius. 


Fig.  131. — Diagram  of  transverse  section  across  the  central  parts  of  the  lateral 
ventricles.     (Cunningham.) 


tributed  to  many  parts  of  the  cerebrum.  External  to  the  internal 
capsule  is  another  nucleus  of  gray  matter  termed  the  lenticular 
nucleus.  It  is  quite  a  large  nucleus,  shaped  somewhat  like  a  bicon- 
vex lens  on  both  transverse  and  horizontal  section.  It  separates 
the  internal  capsule  from  another  layer  of  white  fibers  termed  the 
external  capsule.  Outside  the  external  capsule  is  another  nucleus 
of  gray  matter,  thin  on  transverse  section,  termed  the  claustrum. 

Classification  of  the  Cerebral  Nerve  Tracts  —  The  tracts  of 
white  fibers  of  the  cerebrum  may  be  classed  as  nerve  tracts  con- 
necting the  brain  with  lower  levels.    They  are  afferent  and  efferent. 

Nerve  tracts  connecting  different  portions  of  one  cerebral 
hemisphere. 

Tracts  connecting  two  cerebral  hemispheres. 

The  Afferent  Tracts  of  the  Cerehrum  —  The  thalamo-cortical 

314 


THE  NERVOUS  SYSTEM 


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THE  NERVOUS  SYSTEM 


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320 


THE  NERVOUS  SYSTEM 

,  Central  fissure. 

Posterior  central  gyrus. 
Anterior  central  gyrus. 


Corpus  callosum. 


Fornix. 
Lateral  ventricle. 
Thalamus 

Caudate  nucleus. 
/  Internal  capsule. 


Claustrum. 

Inferior   horn    of 
lat.    vent. 
Hippocampal   fissure. 

Optic  tract. 
Hippocampal  gyrus. 

Uncus. 
Cerebral  peduncle. 

Pons. 
Pyramid  of  medulla  oblongata. 

-View  from  the  front  of  a  coronal  section  of  an  adult  brain  made 
three  inches  behind  the  frontal  pole.     Five-sixths. 

tracts.  From  all  parts  of  the  optic  thalami  fibers  stream  out  into 
the  internal  capsule  to  carry  on  the  impulse  arriving  at  the  optic 
thalami  to  all  parts  of  the  cerebral  cortex.    Entering  the  internal 

322 


THE  NERVOUS  SYSTEM 

capsule  these  fibers  may  be  divided  into  a  frontal,  parietal,  occip- 
ital and  temporal  group. 

The  frontal  filers  are  contained  in  the  anterior  limit  of  the 
internal  capsule  and  run  to  the  frontal  lobe.  Some  of  the  fibers 
pass  to  the  lenticular  nucleus  and  then  other  axons  carry  on  the 
impulses  through  the  external  capsule. 

The  parietal  fibers  issue  from  the  lateral  surface  of  the  optic 
thalami  and  pass  to  the  parietal  lobe  through  the  middle  portions 
of  the  internal  capsule.  The  occipital  fibers  form  radiations  called 
the  occipital  radiations,  and  pass  to  the  occipital  lobe  through  the 
posterior  portion  of  the  internal  capsule,  coming  chiefly  from  the 
pulvinar  or  posterior  tubercle  of  the  optic  thalamus  and  the 
external  geniculate  body. 

The  fibers  issuing  from  the  under  surface  of  the  optic  thalami 
pass  under  the  lenticular  nucleus  to  the  temporal  lobe  and  island 
of  Reil.  Some  of  these  fibers,  known  as  the  auditory  radiations, 
pass  directly  into  the  posterior  portion  of  internal  capsule  from 
the  internal  geniculate  body. 

Functions  of  the  Thalamo-cortical  Fibers  —  Of  these  various 
afferent  fibers,  those  passing  to  the  parietal  lobes  carry  onward  to 
the  cortex  the  cutaneous  and  possibly  muscular  sensations,  reach- 
ing the  optic  thalami  through  the  mesial  fillet.  Also  among  the 
fibers  of  the  anterior  or  middle  portions  of  the  internal  capsule 
are  those  carrying  on  the  impulses  reaching  the  red  nucleus  and 
optic  thalami  by  the  superior  cerebellar  peduncles. 

They  must  be  considered  as  furnishing  information  regarding 
the  fine  adjustments  in  muscular  coordination  being  produced  by 
the  cerebellum.  The  optic  radiations  carry  visual  impulse  from 
the  terminations  of  the  optic  nerve  in  the  superior  corpora  quad- 
rigemina.  By  other  fibers  between  the  occipital  cortex  and  these 
basal  nuclei  impulses  may  pass  from  the  cortex  to  the  superior  cor- 
pora quadrigemina  and  thence  as  afferent  impulses  to  the  cere- 
bellum. Through  the  auditory  radiations  to  the  temporal  lobes 
are  transmitted  impulses  from  the  inferior  corpora  quadrigemina 
and  internal  geniculate  body,  which  nuclei  receive  the  termination 
of  the  lateral  fillet  directly  from  the  auditory  nucleus. 

Other  fibers  pass  between  the  optic  thalamus  and  the  cerebral 
cortex  by  way  of  the  corpus  striatum.  The  larger  portion  of  the 
afferent  fibers  of  this  body  come  from  the  optic  thalami.     Other 

324 


Ganglia  of  sensory  cranial  nerves 


Nucleus    of   spinal    tract    of    trigeminus.  J 


Posterior  root, 
Spinal  ganglion. 


Fasciculus  cuneatus. 


Fasciculus  gracilis. 


rrg.    136. — Scheme    of    ascending    or    spinocerebral    conduction    pathways.     (Morris.) 


THE  NERVOUS  SYSTEM 


Somaesthetlc  area 
of  cerebral  cor- 
tex. 

Caudate  nucleus. 

Internal  capsule. 

Lenticular  nucleus. 

Cerebral  peduncle. 
Trochlear    nerve, 


Medulla    oblongata 


Oculo- 
motor. 

Masti- 
cator. 


Abducens. 

Facial. 

Glossopharyngeal. 

Vagus. 

Accessory. 

Hypoglossal. 


Motor 
nuclei  of 
"   cranial 
nerves. 


Decussation  of  pyramids. 


Lateral  cerebrospinal 

fasciculus. 
Ventral   cerebrospinal 

fasciculus. 


Ventral  roots  of  spinal  nerves. 
Ventral  white  commissure. 


Spinal  cord. 


.'ig.  137.— Scheme  of  descending  cerebrospinal  conduction  pathways.    (Morris.) 


328 


THE  NERVOUS  SYSTEM 

fibers  arising  in  the  corpus  striatum  pass  in  the  dorsal  part  of  the 
crusta  to  the  nuclei  pontis  of  the  formatio  reticularis. 

Connections  undoubtedly  exist  in  both  directions  between  the 
cortex  cerebri  and  the  nuclei  of  the  corpus  striatum.  The  chief 
nucleus  of  the  corpus  striatum  is  the  caudate  nucleus.  The  len- 
ticular nucleus  and  claustrum  form  similar  connections. 

Pyramidal  Tracts  —  The  efferent  tracts  from  the  Gerehrum  — 
The  pyramidal  tract  originates  as  axis  cylinders  of  the  cells  in 
the  ascending  frontal  convolution.  The  fibers  pass  downwards  and 
inwards  through  the  white  matter  of  the  hemispheres  to  the  in- 
ternal capsule.  In  this  structure  they  occupy  the  middle  two- 
fifths  on  transverse  section.  The  internal  capsule  presents  a  bend 
at  the  juncture  of.  the  anterior  one-third  and  posterior  two-thirds, 
with  the  concavity  outwards,  and  surrounds  the  lenticular  nucleus. 
Anterior  to  the  bend  the  caudate  nucleus  lies  internal  to  it  and 
posterior  to  the  bend  the  optic  thalamus  lies  internal  to  it.  The 
pyramidal  fibers  occupy  the  bend  and  the  anterior  two-thirds  of 
the  portion  posterior  to  the  bend.  In  this  portion  the  fibers  con- 
trolling the  muscles  of  the  head  lie  anteriorly,  then  the  fibers 
belonging  to  the  anterior  extremity,  the  trunk  and  posterior  ex- 
tremity. The  pyramidal  fibers  finally  leave  the  internal  capsule 
and  enter  the  crusta  or  crura  cerebri.  These  structures  may  be 
viewed  as  the  stems  of  the  brain.  In  the  mid-brain  they  lie  ventral 
to  the  rest  of  the  mid-brain  and  diverge  as  they  are  traced  upwards 
and  forwards  between  the  mid-brain  and  the  cerebrum,  to  enter  the 
latter  by  forming  the  internal  capsule.  The  two  crusta  thus  fork 
to  inclose  between  them  as  they  enter  the  brain  the  two  optic 
thalami.     (Fig.  137.) 

The  remainder  of  the  mid-brain,  that  is  the  dorsal  portion, 
enters  the  cerebrum  by  passing  directly  into  the  optic  thalami. 
In  the  crusta  the  pyramidal  fibers  form  the  middle  two-fifths  of 
that  structure. 

A  small  portion  of  the  upper  part  of  the  external  surface  of 
the  optic  thalami,  above  the  diverging  fibers  of  internal  capsule, 
lies  free  in  the  beginning  of  the  descending  horn  of  the  lateral 
ventricle. 

Fronto-pontine  Fibers  —  In  the  anterior  limb  of  the  internal 
capsule  other  nerve  fibers,  arising  as  axis  cylinders  of  the  nerve 
cells  in  the  frontal  lobes  of  the  brain,  pass  down  into  the  mesial 

330 


THE  NERVOUS  SYSTEM 

portion  of  the  crusta  and  end  around  the  scattered  cells  in  the 
formatio  reticularis. 

Temporo-pontine  Fibers  —  Other  efferent  fibers  from  the  cere- 
brum arise  in  the  temporal  lobes  and  reach  the  posterior  limb  of 
the  internal  capsule  by  passing  under  the  lenticular  nucleus.  They 
then  reach  the  external  division  of  the  crusta  and  end  in  the  scat- 
tered cells  of  the  pons. 

Both  the  fronto-pontine  and  temporo-pontine  fibers  represent 
efferent  tracts  from  the  cerebrum  and  afferent  to  the  cerebellum 
of  the  cerebro-cerebellar  connections,  being  continued  into  the 
lateral  hemispheres  of  the  cerebellum  by  the  transversely  running 
middle  peduncles.  The  return  tract  of  this  cerebro-cerebellar  con- 
nection is  from  the  cortex  of  cerebellum  to  the  dentate  nucleus, 
then  by  the  superior  peduncles  to  the  red  nucleus  and  optic  thalami, 
and  finally  from  the  optic  thalami  to  the  cerebral  cortex.  Part 
of  the  thalamo-cortical  fibers  have  already  been  described,  those 
passing  directly  into  the  internal  capsule  and  around  the  lenticular 
nucleus  as  the  thalamo-frontal,  thalamo-parietal  and  the  auditory 
and  optic  radiations. 

Intra-Cerebral  Association  Tracts  —  Short  and  long  association 
tracts  exist  within  the  cerebrum.  The  short  tracts  pass  in  U-shaped 
loops  between  the  various  convolutions  around  the  bottom  of  the 
sulci.  The  long  tracts  may  be  divided  into  longitudinal  tracts  and 
commissural  tracts.     The  longitudinal  tracts  are: 

Uncinate  fasciculus  —  Between  the  orbital  convolutions  of  the 
frontal  lobes  and  the  front  part  of  the  temporal  lobes,  around  the 
bottom  of  the  fissure  of  Sylvius. 

The  cingulum  —  From  the  anterior  perforated  space  over  the 
dorsum  of  the  corpus  striatum  to  the  hippocampus  major  and  an- 
terior part  of  temporal  lobe.     (Fig.  138.) 

Superior  longitudinal  fasciculus  —  Somewhat  the  same  course 
as  the  cingulum,  connecting  the  frontal  parietal  and  occipital 
lohes. 

Inferior  longitudinal  fasciculus  —  External  to  the  optic  radia- 
tion between  the  temporal  and  occipital  lo'hes. 

Occipito- frontal  fasciculus  —  Runs  close  to  caudate  nucleus  in 
outer  walls  of  lateral  ventricle. 

The  commissural  fibers  include : 

(a)     The  great  mass  of  cortical  fibers  running  between  the 

332 


THE  NERVOUS  SYSTEM 


-C3 


f^ 


334 


THE  NERVOUS  SYSTEM 

two  hemispheres  and  constituting  the  major  portion  of  the  corpus 
callosum. 

(b)  The  anterior  commissure,  connecting  the  two  olfactory 
lobes  and  portions  of  the  two  temporal  lobes. 

(c)  Middle  commissure,  between  the  optic  thalami. 

(d)  The  hippocampal  commissure,  a  thin  lamina  between  the 
diverging  posterior  pillars  of  the  fornix,  appears  on  the  under 
surface  of  the  corpus  callosum,  connecting  the  two  hippocampi 
majora. 

FUNCTIONS  AND  CONNECTIONS  OF  THE  CRANIAL  NERVES 

Olfactory  Nerves  —  The  olfactory  as  the  optic  nerves  are  to  be 
viewed  as  cerebral  associated  tracts  connecting  the  brain  with  a 
more  distal  portion  of  this  same  organ. 

Anatomically  they  are  different  from  the  other  cranial  nerves. 

The  olfactory  nerve  fibers  are  derived  from  cells  situated  upon 
the  surface  of  the  body  imbedded  within  the  nasal  mucous  mem- 
brane. One  process,  the  real  olfactory  nerve,  passes  forward  toward 
the  surface  to  end  in  the  olfactory  end  sense  organ.  The  other 
process  passes  backward  as  a  medullated  nerve  fiber,  through  the 
cribriform  plate  to  the  olfactory  bulb,  where  they  terminate  in  a 
terminal  arborization  among  the  branches  of  another  terminal 
arborization  of  the  peripheral  process  of  another  nerve  cell  called 
a  mitral  cell. 

It  is  the  axons  of  the  mitral  cells  which  form  the  olfactory 
tracts.  Each  tract  divides  posteriorly  into  two  roots,  a  mesial 
root  ending  in  the  anterior  end  of  the  callosal  gyrus  of  the  limbic 
lobe,  and  a  lateral  root,  crossing  the  anterior  perforated  space  to 
end  in  the  uncinate  extremity  of  the  hippocampal  gyrus.  Between 
these  two  tracts  is  a  prominence,  the  olfactory  tubercle. 

Portions  of  the  Brain  Forming  the  Olfactory  Mechanism  — 
The  following  portions  of  the  brain  serve  as  central  nuclei  and 
association  tracts  of  the  olfactory  apparatus. 

(1)  Olfactory  bulb  and  tract. 

(2)  Anterior  perforated  space. 

(3)  Anterior  portion  of  the  uncinate  gyrus. 

(4)  Septum  lucidum. 

(5)  Hippocampal  convolution. 

336 


THE  NERVOUS  SYSTEIM 


(6) 
(7) 
(8) 
(9) 
(10) 

(11) 


Anterior  commissure. 

Trigonum  habenulae. 

Fornix. 

Corpora  mammillaria. 

The  bundle  of  Vicq  d'Azyr. 

Optic  thalami. 


Fig.  139. — Diagram  of  the  principal  components  of  the  optic  apparatus. 

(Morris.) 

The  Optic  Nerve  —  The  real  optic  nerves  are  merely  the  short 
processes  of  nerve  cells,  situated  within  the  retina  and  passing 
to  the  sensory  epithelium  of  the  retina.  The  central  processes  of 
these  nerve  cells  pass  in  the  opposite  direction  and  form  the  optic 
tracts.     These  partially  decussate  in  the  optic  chiasma  in  such  a 

338 


THE  NERVOUS  SYSTEM 

manner  that  only  the  fibers  from  the  internal  half  of  each  retina 
cross.  The  optic  tracts  end  posteriorly  in  the  pulvinar  of  the 
optic  thalami,  the  external  geniculate  body  and  the  superior  cor- 
pora quadrigemina.  From  these  connections  nerve  fibers  enter  the 
posterior  portion  of  the  internal  capsule  and  pass  by  the  optic 
radiations  to  the  occipital  lobes.  This  nerve  transmits  visual 
sensations. 


MUCL.1.W. 
{OARKSCtiewrrsCH;  \       \ 


WUCU.VENT.I,  (nHT.) 


NUCL.OORS.II.(POSx; 
(V.CUOOEN) 


NUCUCEMTRAUS- 

,NueuviNr.ii.(posT.) 


Fig.   140. — Diagram  of  the  groups   of  cells  forming  the  nuclei   of  the  third 
and  fourth  nerves.     (Quain.) 
The  fibres  from  the  nucleus  of  Darkschewitsch  to  the  oculo-motor  nerve 
are  doubtful. 


The  Third,  Fourth  and  Sixth  Nerves  —  The  third  and  fourth 
and  sixth  nerves  may  be  regarded  as  arising  from  one  continuous 
elongated  nucleus,  extending  from  the  level  of  the  strife  acusticse 
in  the  fourth  ventricle  to  the  superior  corpora  quadrigemina,  close 
to  the  middle  line. 

The  anterior  portion  of  this  nucleus,  that  belonging  to  the 
third  nerve,  may  be  divided  into  different  portions,  a  more  lateral 
large-cell  portion,  a  superficial  small-cell  portion  and  another 
median  portion  of  large  cells.     (Figs.  140  and  141.) 

Stimulation  from  before  backward  beginning  at  the  posterior 

340 


THE  NERVOUS  SYSTEM 

boundary  of  the  third  ventricle  gives  contraction  of  the  ciliary 
muscle  (changing  the  curvature  of  the  lens  of  the  eye),  contraction 
of  the  pupil,  of  the  internal  rectus,  the  superior  rectus,  the  levator 
palpebr^e  superioris,  the  inferior  rectus  and  the  inferior  oblique. 
Finally,  when  the  nucleus  of  the  fourth  nerve  is  reached,  we  obtain 
contraction  of  the  superior  oblique,  and  when  the  sixth  nerve  is 
reached,  contraction  of  the  external  rectus. 


nm 


Fig.  141. — Section  through  the  upper  part  of  one  of  the  anterior  corpora 
quadrigemina  and  the  adjacent  part  of  the  thalamus.  (Quain.) 
s.,  aqueduct;  gr.,  gray  matter  of  aqueduct;  c.  g. s.,  quadrigeminal  emi- 
nence, consisting  of:  I.,  stratum  lemnisci;  o.,  stratum  opticum;  and  c,  stratum 
cinereum;  Th.,  thalamus  (pulvinar) ;  c.g.i.,  c.g.e.,  internal  and  external 
(mesial  and  lateral)  geniculate  bodies;  br.s.,  br.i.,  superior  and  inferior 
brachia;  j.,  fillet;  p.  I.,  posterior  (dorsal)  longitudinal  bundle;  r.,  raphe;  ///, 
third  nerve;  nlll,  its  nucleus;  I. p. p.,  posterior  perforated  space;  s.n.,  sub- 
stantia nigra;  above  this  is  the  tegmentum  with  its  nucleus,  the  latter  being 
indicated  by  the  circular  area;  cr.,  crusta;  II,  optic  tract;  M.,  medullary 
centre  of  the  hemisphere;  n.c,  nucleus  caudatus;  st.,  stria  terminalis. 


All  these  nuclei,  as  also  the  endings  of  the  optic  nerves  in  the 
superior  corpora  quadrigemina,  are  connected  by  means  of  the 
posterior  longitudinal  bundle,  so  that  means  are  provided  for 
accurate  coordination,  not  only  between  the  oculo-motor  nuclei 
themselves,  but  because  many  of  the  fibers  of  the  posterior  longi- 
tudinal bundle  are  axons  of  cells  of  Deiters'  nucleus,  with  also 

342 


THE  NERVOUS  SYSTEM 

the  great  centers  of  coordinatiou  of  the  whole  body  in  the  cere- 
bellum. 

The  important  tract  between  the  superior  corpora  quadrigemina 
and  the  cerebellum  indicate  that  the  connections  of  the  former 
with  the  optic  nerves  chiefly  serve  the  function  of  coordination  of 
visual  impulses  with  the  movements,  not  only  of  the  eye,  but  also 
of  the  rest  of  the  body. 

The  function  of  the  oeulo-motor  nerves  is  not  entirely  motor. 
They  contain  a  large  proportion  of  afferent  fibers  from  the  muscle 
of  the  eye-ball.  After  total  desensitization  of  the  eye-ball  by 
cocaine  or  by  section  of  the  fifth  nerve,  the  movements  of  the 
eye-ball  will  be  carried  out  with  as  much  precision  as  under  normal 
conditions. 

The  Fifth  Nerve  —  The  fifth  nerve  is  both  motor  and  sensory. 
It  supplies  sensation  from  the  whole  of  the  face  and  interior  of 
the  mouth.  Its  motor  fibers  supply  the  muscles  of  mastication. 
It  also  supplies  the  tensor  tympani  muscle.  It  contains  trophic 
fibers. 

The  Seventh  Nerve  —  The  seventh  cranial  nerve  is  largely 
motor  to  the  muscles  of  the  face  and  some  of  the  internal  ear 
muscles.  Through  the  nervus  intermedins  of  Wrisberg,  which  is 
usually  included  as  part  of  the  seventh  nerve  but  should  really 
be  considered  a  separate  nerve  containing  efferent  secretory  fibers 
to  the  submaxillary  and  sublingual  glands  and  afferent  fibers,  con- 
veying impulses  of  taste  and  general  sensibility  from,  the  tongue 
backwards  from  the  geniculate  ganglion. 

The  Eighth  Nerve  —  The  eighth  nerve  possesses  two  definite 
functions.  Its  auditory  branch  carries  impulses  from  the  sensory 
auditory  epithelium.  Its  fibers  originate  in  the  bipolar  cells  of 
the  ganglion  of  Scarpa. 

The  nerve  enters  the  medulla  immediately  beneath  the  pons,  and 
terminates  in  its  dorsal  and  its  ventral  nucleus.  From  these  nuclei 
the  auditory  impulses  pass  to  the  brain  by  way  of  the  trapezium, 
the  lateral  fillet,  the  inferior  corpora  quadrigemina  and  the  audi- 
tory radiations.  The  vestibular  branch  originates  in  the  ganglion 
of  the  cochlea.  The  peripheral  processes  of  these  cells  end  in  the 
sensory  epithelium  of  the  ampulla  of  the  semicircular  canals  and 
of  the  saccule  and  utricle.  (Fig.  142.)  The  nerve  enters  the  me- 
dulla with  the  auditory  division  and  passes  to  the  dorsal  nucleus 

344 


THE  NERVOUS  SYSTEM 


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ca  (3  cj 


01  K  ■ 


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bO 


346 


^  THE  NERVOUS  SYSTEM 

beneath  the  trigonum  acusticum.  It  makes  connections  with  the 
nucleus  of  Dieters  and  Bechterew.  Some  of  its  fibers  pass  directly 
to  the  cerebellum.  The  vestibular  never  transmits  only  sensations 
of  equilibrium.  Thus  it  is  that  its  most  important  connections  are 
with  the  cerebellum,  that  central  mass  of  gray  matter  the  chief 
function  of  which  is  to  preside  over  equilibrium.  Through  the 
vestibulo-spinal  tract  the  vestibular  impulses  affect  the  spinal 
centers. 

Through  the  posterior  longitudinal  bundle  the  nuclei  of  the 
third,  fourth  and  sixth  nerves  become  coordinated  with  the  ves- 
tibular impulses,  and  through  the  superior  cerebellar  peduncle 
by  way  of  the  red  nucleus  and  optic  thalamus  these  same  impulses 
reach  the  cerebral  cortex  and  excite  there  efferent  motor  impulses 
which  may  still  further  influence  the  motor  mechanism  of  the 
spinal  cord. 

The  Ninth  Nerve  —  The  ninth  and  tenth  cranial  nerves  are 
chiefly  sensory.  The  central  nuclei  form  one  continuous  column 
lateral  to  the  motor  nuclei  beneath  the  floor  of  the  fourth  ven- 
tricle. Both  these  nerves  contain  efferent  fibers  arising  from 
nuclei  internal  and  ventral  to  the  sensory  nuclei.  The  chief  motor 
nucleus  of  the  tenth  nerve  is  the  nucleus  ambiguus. 

The  following  are  the  functions  of  the  ninth  cranial  nerve: 

(1)  Motor  to  the  muscles  of  the  pharynx  and  base  of  the  tongue. 

(2)  Secretory  fibers  to  the  parotid  gland  by  way  of  the  optic 
ganglion.  (3)  Sensory  fibers  from  the  tongue,  mouth  and  pharynx. 
(4)  Inhibitory  fibers  to  the  respiratory  center. 

The  Tenth  Nerve  —  The  tenth  or  pneumogastric  nerve  is  the 
longest  nerve  in  the  body.  Its  connections  are  most  numerous 
and  its  functions  more  varied  and  important  than,  perhaps,  any 
other  single  nerve. 

Its  efferent  functions  are:  (1)  Motor  to  the  levator  paiati  and 
three  constrictors  of  pharynx.  (2)  Motor  to  larynx.  (3)  Inhib- 
itory to  the  heart.  (4)  Motor  to  muscles  of  esophagus,  stomach, 
and  small  intestines.  (5)  Motor  to  unstriated  muscle  in  the  walls 
of  the  bronchi  and  bronchioles.  (6)  Secretory  to  glands  of  stomach 
and  possibly  pancreas. 

Its  afferent  functions  are:  (1)  Regulate  inspiration,  accelerate 
and  promote  inspiration  or  increase  expiration  as  in  coughing.     (2) 

348 


THE  NERVOUS  SYSTEM 

Depressor  and  pressor  from  heart  to  vasomotor  center.  (3)  Ke- 
flex inhibition  of  the  heart. 

The  Eleventh  Nerve  —  The  eleventh  or  spinal  accessory  nerve 
should  not  be  considered  as  a  cranial  nerve.  Filaments  enter  it 
which  take  origin  by  series  of  roots  coming  from  cells  in  the  in- 
terior horn  of  cord  as  low  down  as  the  sixth  cervical  nerve  (spinal 
portion),  but  continuous  above  with  those  of  the  accessory  por- 
tion. It  is  a  purely  motor  nerve  to  the  trapezius  and  sterno- 
mastoid  muscle. 

The  Tw^elfth  Nerve  —  The  twelfth  cranial  nerve  arises  from 
cells  under  the  trigonum  hypoglossi  in  the  floor  of  the  lower  half 
of  the  fourth  ventricle.  It  is  purely  motor  in  function,  supplying 
the  muscles  of  the  tongue  and  those  muscles  attached  to  the  hyoid 
bone  and  the  extrinsic  muscles  of  the  larynx. 

THE  FUNCTIONS  OP  THE  VARIOUS  PORTIONS  OF  THE  BRAIN 

Methods  of  Study  —  Several  methods  are  available  for  investi- 
gating the  functions  of  the  brain. 

(1)  A  knowledge  of  the  anatomical  connections  of  the  tracts 
within  the  brain  furnishes  in  itself  information  upon  the  functions 
of  the  brain  which  is  second  to  none  in  importance.  It  is  for 
this  reason  that  a  detailed  study  of  the  anatomy  of  the  brain  has 
been  necessary. 

(2)  Considerable  information  upon  the  function  of  various 
portions  of  the  brain  is  available  from  a  study  of  the  differences  in 
the  histological  structure  of  the  brain. 

(3)  Direct  experimentation  by  isolation  or  ablation  of  por- 
tions of  the  brain  enable  us  to  know  the  function  of  the  portion 
operated  upon. 

(4)  The  study  of  the  symptoms  of  human  beings  affected  with 
tumors  or  other  diseases  of  the  brain  producing  its  destruction. 

The  function  of  any  portion  of  the  brain  must  depend  solely 
upon  the  efferent  tracts  which  leave  it  and  the  afferent  tracts 
entering  it. 

We  have  seen  that  the  animal  with  only  a  spinal  cord  is  a 
machine  for  the  performance  of  certain  reflexes.  The  reflexes 
involve  particularly  muscles  belonging  to  the  same  level  as  the 
stimulated  afferent  nerves.     They  are  inevitable  and  contain  no 

350 


THE  NERVOUS  SYSTEM 

incalculable   element.     The  frog  is  best  adapted   for   an  experi- 
mental investigation  of  such  a  character. 

If  we  investigate  in  this  manner  the  brain  we  begin  by  divid- 
ing the  bulb  by  a  section  between  the  medulla  and  pons.  Such 
an  animal  is  called  the  bulbo-spinal  animal.  It  will  present  cer- 
tain phenomena  not  present  in  the  spinal  animal  and  determined 
by  the  character  of  the  afferent  nerves  having  their  nuclei  in 
the  bulb. 

The  Afferent  Impulses  Received  by  the  Medulla  —  The  bulb 
receives:  (1)  Afferent  impressions  of  taste  from  the  tongue  through 
the  nervus  intermedins.  (2)  Through  the  ninth,  afferent  impres- 
sions from  the  tongue  and  pharynx.  (3)  Through  the  vagus  affer- 
ent impulses  from  the  whole  alimentary  canal  to  the  ileocolic 
sphincter  and  from  the  lungs  and  heart. 

Efferent  Impulses  Passing  from  the  Medulla  —  It  also  sends 
efferent  fibers  from  the  nucleus  ambiguus  to  the  larynx,  bronchi, 
esophagus,  stomach  and  intestines,  secretory  fibers  to  the  stomach 
and  inhibitory  fibers  to  the  heart. 

The  eighth  nerve  is  divided,  even  if  all  of  its  nucleus  is  not  by 
the  seetidn.  The  twelfth  nerve  supplying  the  muscles  of  the 
tongue  is  preserved. 

The  Bulbo-Spinal  Animal  and  How  It  Differs  from  the  Spinal 
Animal  —  The  preservation  of  these  additional  centers  makes  it 
possible  for  the  bulbo-spinal  animal  to  maintain  those  visceral 
functions  which  are  under  the  nervous  control  of  the  bulb.  The 
blood  pressure  will  not  show  the  great  fall  present  in  the  spinal 
animal.  The  animal  will  also  continue  to  breathe  regularly  and 
its  heart  rate  will  remain  normal.  All  these  functions  may  be 
affected  by  appropriate  stimuli. 

There  is,  moreover,  a  certain,  though  ill  defined,  dependence 
of  the  skeletal  muscles  upon  the  visceral  functions;  so  that,  with 
the  preservation  of  the  visceral  nervous  control,  there  is  a  greater 
stability  in  the  response  of  the  bulbo-spinal  animal  to  reflexes. 

It  is  easier  to  evoke  movements  in  all  four  limbs.  The  key 
to  the  situation  is  the  preservation  of  visceral  functions  and  the 
nexus  between  these  and  the  skeletal  motor  functions.  The  mech- 
anism by  which  food,  including  oxygen,  is  seized,  tasted,  swallowed 
and  digested  and  its  distributions  in  part  controlled  is  preserved. 
If  in  the  frog  the  eighth  nerve  has  been  left  intact  a  certain  amount 

352 


THE  NERVOUS  SYSTEM 

of  the  sense  of  equilibrium  is  preserved.  The  animal  will  try  to 
right  itself  if  laid  on  its  back,  and  usually  succeeds. 

The  Pontine  Bulbo-Spinal  Animal  — In  order  to  investigate 
these  the  brain  must  be  divided  by  a  section  at  the  upper  border 
of  the  pons.  The  motor  nuclei  of  the  fifth  and  sixth  nerves  have 
now  been  preserved,  as  have  the  lower  nuclei  of  the  organ  of  hear- 
ing and  the  important  organ  of  static  sense,  the  nucleus  of  the 
vestibular  branch  of  the  eighth  nerve.  Such  an  animal  is  able  to 
walk,  spring  and  swim.  When  placed  on  its  back  it  immediately 
turns  over  and  will  appreciate  the  rotation  of  a  turn-table,  when 
placed  upon  it,  by  turning  its  eyes  in  the  opposite  direction. 

The  controlling  influence  of  the  cerebellum  upon  the  independ- 
ently excessive  excitability  of  the  lower  centers  is  made  evident 
by  its  removal  from  the  pontine-spinal  animal.  If  after  section 
above  the  pons  the  cerebellum  is  also  removed,  the  animal  be- 
comes spontaneously  active,  crawling  about  until  blocked  by  some 
obstacle.  There  is  also  an  increased  activity  of  the  swallowing 
reflex,  anything  touching  the  mouth  is  snapped  at. 

In  the  mammal  there  is  a  similar  increase  of  reflex  activity, 
but  the  power  of  progression  is  not  retained. 

The  Animal  Possessing  the  Brain  and  Cord,  All  Below  the 
Upper  Level  of  the  Mid-Brain  —  The  Functions  of  the  Mid-Brain 
—  AVhen  the  mid-brain  is  preserved  by  a  section  in  front  of  the 
anterior  corpora  quadrigemina,  the  animal  will  be  in  possession  of 
all  its  sensory  impressions  and  the  efferent  paths  to  all  the  eye 
muscles  except  the  olfactory  sense.  In  the  mammal  such  a  con- 
dition causes  "decerebrate  rigidity."  The  limbs  are  held  more 
or  less  rigidly  in  a  position  of  extension  and  resist  passive  flexion. 
The  condition  would  appear  to  be  due  in  part  to  the  increased 
activity  of  the  lower  centers,  especially  of  the  cerebellum,  and  is 
reflex,  as  it  is  at  once  abolished  by  section  of  the  posterior  spinal 
roots,  and  in  part  to  the  removal  of  the  inhibitory  impulses  nor- 
mally flowing  through  the  cerebro-spinal  tracts.  It  must  be  re- 
membered the  pyramidal  tracts  in  the  frog  are  represented  by 
only  a  few  fibers. 

The  Animal  Possessing  the  Optic  Thalami,  All  the  Brain  and 
Cord  BeloM^  Them  —  The  preservation  of  the  optic  thalami,  that 
is,  the  removal  of  the  cerebral  hemispheres  alone,  leaves  the  frog 
with  all  that  is  necessary  for  the  response  to  any  stimulus.     Un- 

354 


THE  NERVOUS  SYSTEM 

less  the  animal  is  observed  critically  one  would  fail  to  notice  any- 
thing wrong  with  the  animal.  It  sits  up  in  its  position,  on  inter- 
ference jumps  away,  guides  itself  perfectly  by  sight.  It  will 
swim  about  in  water  until  it  finds  a  support  upon  which  it  will 
crawl  out.  It  will  crawl  up  an  inclined  board  and  if  the  inclination 
is  gradually  increased  until  the  board  is  rotated  on  its  lower  end, 
the  frog  will  crawl  up  one  side  and  down  the  other. 

The  single  difference  between  such  an  animal  and  the  normal 
animal  is  the  entire  absence  in  the  former  of  spontaneous  motion. 
It  is  an  extremely  complex  and,  in  contrast  to  the  previously  de- 
scribed animal,  an  extremely  accurate  and  well-balanced  machine. 
Every  movement,  however,  must  be  provoked  by  a  closely  related 
external  stimulus. 

If  care  has  been  taken  to  preserve  the  optic  thalami  in  such  an 
animal  it  will  occasionally  show  spontaneous  movements,  such,  for 
instance,  as  attempts  to  bury  itself  as  if  to  hibernate  upon  the 
approach  of  winter.  If  the  optic  thalami  have  been  preserved  in 
fishes  they  show  very  little  difference  from  the  normal  fish. 

On  the  other  hand,  elasmobranch  fishes  which  depend  mainly 
upon  the  olfactory  apparatus,  the  removal  of  merely  the  olfactory 
lobes  and  cerebral  hemispheres  produce  almost  complete  paralysis, 
even  though  the  optic  lobes  and  thalami  are  intact. 

The  animal  contains  no  incalculable  element.  It  feels  no  hunger 
or  fear.  The  bird  acts  much  as  the  frog.  It  is  able  to  walk  about 
avoiding  obstacles  and  even  to  fly.  It  is  unable  to  recognize  food 
or  enemies  or  its  opposite  sex.    It  shows  no  fear. 

The  whole  of  the  cerebral  hemispheres  have  been  successfully 
removed  in  a  dog.  It  was  able  to  walk  normally  and  spent  most 
of  the  day  in  walking  up  and  down  its  cage.  It  slept  soundly  at 
night.  In  pinching  its  skin  it  would  turn  around  and  snarl  and 
attempt  to  bite.  It  could  not  recognize  food,  showed  no  fear  or 
pleasure  or  recognition  of  those  who  fed  it.  All  memory  was 
gone. 

Functions  of  the  Cerebellum  —  We  have  seen  that  there  are 
two  distinct  classes  of  afferent  stimuli;  we  may  speak  of  them  as 
two  systems  of  afferent  nerves. 

1.  Exteroceptive  or  stimuli  coming  from  the  surface  of  the 
body  or  striking  it  from  a  distance. 

2,  Proprioceptive  or  afferent  stimuli  from  the  interior  of  the 

356 


THE  NERVOUS  SYSTEM 


body,  the  muscles,  joints  and  tendons.  This  second  system  has  its 
head  ganglion  in  the .  cerebellum.  By  its  afferent  nerves  it  fur- 
nishes information  as  to  the  exact  position  of  the  limbs  and  the 
degree  of  contraction  of  the  muscles.  As  a  part  of  this  system 
must  be  included  the  afferent  stimuli  entering  the  vestibular  branch 
of  the  eighth  nerve,  conveying  those  impressions  of  static  sense 
which  have  reference  to  the  body  as  a  whole. 

The  head  ganglion  of 
this  system  is  the  cerebel- 
lum. All  its  impressions 
are  received  and  properly 
balanced  against  one  an- 
other in  this  organ  and 
just  the  correct  efferent 
impulses  discharged  to  the 
higher  parts  of  the  central 
nervous  system,  but  also 
indirectly  to  the  spinal 
cord  through  the  vestibulo- 
spinal tract  and  the  cere- 
bro-spinal  tracts,  to  pro- 
duce just  that  proper  de- 
gree of  relative  contrac- 
tion and  relaxation  of  op- 
posing sets  of  muscles 
which  will  result  in  a  per- 
fection of  coordination,  not 
only  in  the  normal  tone 
preserved  during  rest  but 
also  in  the  variations  of  contractions  incidental  to  the  muscular 
activities,  which  are  superimposed  by  the  higher  parts  of  the  cen- 
tral nervous  system  or  by  the  pure  reflexes  of  the  spinal  cord. 

The  Histology  of  the  Cerebellar  Cortex  —  The  cortex  of  the 
cerebellum  consists  of  the  following  two  layers  between  which  are 
situated  cells,  called  the  cells  of  Purkinje:    (Figs.  143  and  144.) 

1.  Molecular  layer  —  Most  external,  its  characteristic  cell  is 
star-shaped  with  an  axon  which  runs  parallel  with  the  surface. 
Prom  this  axon  collateral  fibers  dip  internally,  to  end  in  a  regular 
basket-like  arborization  around  the  cells  of  Purkinje. 

358 


143. — Cells    of   the    cerebellar   cortex, 
showing   the   probable   path    of 
nerve-impulses.     (Quain.) 
A,  a  moss-fibre  (afferent) ;  B,  an  axon  of 
a  Purkinje  cell    (efferent);   a,  granules;    b, 
their  axons;  c,  a  Golgi  cell;  d,  two  Purkinje 
cells. 


THE  NERVOUS  SYSTEM 


2.     Granular  or  nuclear  layer  —  It  contains  two  kinds  of  cells : 

(a)     Small   cells   with   dendrites   and    one   axon   which   runs 

straight  up  into  the  molecular  layer  where  it  bifurcates  into  two 

branches  running  parallel  to  the  surface  and  resting  upon  the  tips 

of  the  tree  like  arborization  of 
Purkinje's  cells. 

(&)  Golgi's  cells  —  Cells  with 
many  dendrites  terminating  in 
the  neighboring  gray  matter. 

There  are  two  sets  of  affer- 
ent fibers  to  the  cerebellar  cor- 
tex and  one  set  of  efferent  fibers. 

1.  Moss  fibers  —  Afferent 
fibers  presenting  curious  thick- 
enings and  terminating  by  fre- 
quent branches  in  the  gray  mat- 
ter. 

2.  Tendril  fibers,  also  affer- 
ent ending  by  arborization 
around  the  base  of  the  cells  of 
Purkinje. 

3.  Axons  of  the  cells  of 
Purkinje  run  down  into  the 
white  matter  to  end  around  the 
cells  of  the  deep  nuclei.  No  ef- 
ferent fiber  from  the  cortex  of 
the  cerebellum  leaves  the  cere- 
bellum. 

The  cells  of  Purkinje  are 
large,  flask-shaped  cells  with  one 
apical  dendrite  and  one  axon 
from  the  base  of  the  cell.  The 
one  dendrite  is  characterized  by 


Fig.  144. — Section  of  cortex  of  cere- 
bellum. (Quain.) 
a,  pia  mater;  b,  external  layer;  c, 
layer  of  corpuscles  of  Purkinje;  d, 
inner  or  granule  layer;  e,  medullary 
centre. 


the  richness  of  its  branching. 

The  Afferent  Tracts  to  the  Cerebellum  by  Way  of  the  Three 
Peduncles  —  The  afferent  tracts  of  the  cerebellum  are : 

Inferior  Peduncle  —  ( 1 )  Axons  of  Clark 's  column  of  cells  by 
posterior  cerebellar  tract. 

(2)     From  the  nuclei  gracilis  and  cuneatus  of  the  same  and 
opposite  side. 

360 


THE  NERVOUS  SYSTEM 

(3)  From  vestibular  nerve  directly  and  indirectly  from 
Deiters'  nucleus. 

(4)  Inferior  olive  of  chiefly  the  opposite  side. 

Middle  Peduncle  —  Partly  afferent  and  partly  efferent  to  and 
from  the  formatio  reticularis.  By  means  of  the  nuclei  of  the 
formatio  reticularis  connections  are  established  between  the  frontal 
and  temporal  lobes  of  the  brain. 

Superior  Peduncle — (1)  From  the  superior  corpora  quad- 
rigemina  to  the  cortical  gray  matter,  and  thus  connections  are  es- 
tablished between  the  optic  nerve  and  oculo-motor  and  the  cere- 
bellum. 

(2)     The  anterior  cerebellar  tract  from  the  spinal  cord. 

The  Efferent  Tracts  from  the  Cerehellum  —  Prom  the  roof 
ganglia  the  impulses  from  the  termination  of  the  axons  of  the  cells 
of  Purkinje  are  passed  on  to  the  pons  by  the  middle  peduncle  and 
by  the  superior  cerebellar  peduncle  to  the  red  nucleus  and  subthal- 
amic region.  Fibers  also  pass  from  the  roof  nuclei  to  the  superior 
corpora  quadrigemina. 

No  tract  runs  directly  from  the  cerebellum  to  the  cord,  but 
from  Deiters'  nucleus,  which  is  closely  connected  with  the  roof 
nuclei  of  the  cerebellum,  fibers  run  downward  to  the  cord  in  the 
vestibulo-spinal  tract. 

Muscular  movements  may  be  excited  by  stimulation  of  the 
cerebellum.  Unless  very  strong  stimuli  are  applied  to  the  cortex 
of  the  cerebellum  no  movements  are  excited.  It  is  not  likely, 
therefore,  that  any  of  the  cerebellar  efferent  fibers  leave  the  cortex. 
On  the  other  hand,  when  weak  stimuli  are  applied  to  the  central 
nuclei  movements  are  excited.  Stimulations  of  the  roof  nuclei 
will  produce  movements  of  the  eyes  and  head. 

Stimulation  of  the  nuclei  of  the  lateral  lobes,  the  nucleus 
dentatum,  will  produce  movements  of  the  trunk  and  limbs.  The 
movements  evoked  are  concerned  in  maintaining  equilibrium  and 
involve  every  muscle  of  the  body. 

Behavior  of  the  Cerebellarless  Animal  —  The  functions  of  the 
cerebellum  are  made  more  clear  by  removing  it  in  whole  or  in 
part.  Complete  unilateral  extirpation  of  the  cerebellum  leaves  the 
animal  (e.  g.,  the  dog)  with  three  cardinal  symptoms: 

(1)  Asthenia  or  loss  of  power  on  the  same  side  of  the  body. 

(2)  Atonia  —  considerable  loss  of  tone  on  the  same  side. 

362 


THE  NERVOUS  SYSTEM 

(3)  Astasia, —  tremors,  or  rhythmical  movements,  accompany- 
ing any  voluntary  movement.  A  dog  deprived  of  the  cerebellum 
upon  one  side  at  first  is  unable  to  stand  but  later  acquires  the 
power  to  walk,  though  the  hind  leg  drops  and  tremors  accompany 
every  movement.  The  animal  tends  to  fall  toward  the  side  of  the 
lesion.  It  attempts  to  support  itself  against  any  wall, or  support. 
"When  the  whole  cerebellum  has  been  removed  the  animal  is  unable 
to  walk  for  months.  After  a  time  it  learns  to  do  so  but  shows 
an  ataxia  which  is  quite  different  from  spinal  ataxia  and  may  best 
be  described  as  a  top-heavy  ataxia.  It  is  an  ataxia  precisely  similar 
to  the  staggering  of  a  drunken  man.  The  compensation,  which  is 
acquired  after  cerebellar  lesions,  is  of  cerebral  origin.  Subsequent 
removal  of  the  hemispheres  produces  permanent  inability  to  walk. 
The  animal  or  human  being  without  a  functionating  cerebellum  is 
without  those  impulses  which  normally  constantly  stream  out  from 
it  in  response  to  the  afferent  impulses  of  the  proprioceptive  system 
and  either  directly  or  indirectly  reach  the  cord. 

In  attempting  to  furnish  an  explanation  of  the  symptoms  of 
the  cerebellarless  animal  a  number  of  possibilities  are  present,  all 
of  which  are  possible  factors.  We  have  in  the  first  place  not  merely 
an  interruption  of  a  large  portion  of  the  impulses  conveying  mus- 
cular sensations  and  of  proprioceptive  impulses  of  equilibrium 
through  the  vestibular  nerve  to  the  cerebellum,  but  also  a  loss 
of  what  is  of  greater  importance :  the  operations  of  the  mechanism 
which  gathers  up  all  the  afferent  impulses  expressing  the  state 
of  contraction  of  the  individual  muscles  and  the  relation  of  the 
center  of  gravity  of  the  whole  body  to  its  position,  and  which  sends 
out  as  its  response  to  these  incoming  muscular  impulses  a  constant 
call  upon  the  apparatus  of  the  more  peripheral  portion  of  the  ner- 
vous system  for  just  the  right  degree  of  contraction  and  relaxation, 
or  of  augmentation  and  inhibition,  which  affords  the  tone  of  rest 
and  the  steadying  of  the  changing  phases  of  muscular  activities. 

In  response  to  the  same  incoming  impulses  there  passes  to  the 
higher  portions  of  the  nervous  system  a  unified  call  as  though  from 
the  operations  of  a  clearing-house,  for  the  correct  adjustment  of 
voluntary  movement  to  the  preservation  of  the  desired  position  of 
the  center  of  gravity.  The  failure  in  this  apparatus  leaves  the 
animal  without  its  most  important  guide  in  the  adjustment  of  its 
movements.     In  its  absence  the  animal  must  fall  back  upon  the 

364 


THE  NERVOUS  SYSTEM 

cerebrum  which  is  incompletely  furnished  with  proprioceptive 
muscular  sensations  and  which  lacks  that  superlative  degree  of 
association  of  all  tracts  concerned  in  muscular  movements  which 
exists  in  the  cerebellum. 

Attempts  have  been  made  to  show  by  some  observers  that  the 
normal  activity  of  the  cerebellum  is  exerted  rather  on  the  side  of 
augmentation  of  muscular  function  (Starling)  and  by  others  on 
the  side  of  restraint  of  muscular  function  (Meyers,  J.  A.  M.  A., 
LXV,  16,  1348).  The  latter  idea  explains  better  the  condition  of 
decerebrate  rigidity  following  section  of  the  mid-brain  anterior  to 
the  superior  corpora  quadrigemina,  the  symptom  of  adiadokocinesis, 
and  the  spontaneous  activity  of  the  frog  after  removal  of  the  cere- 
bellum and  section  of  the  brain  in  front  of  the  pons. 

However  this  may  be,  the  greatest  emphasis  should  be  laid  on 
the  fact  that  the  supreme  function  of  the  cerebellum  is  the  exercise 
of  a  control  over  muscular  contraction,  which  control  has,  so  to 
speak,  for  its  aim  the  production  of  a  perfect  coordination  in  both 
states  of  rest  and  states  of  changing  muscular  activity. 

In  states  of  rest  coodination  is  provided  for  through  the  more 
direct  spinal  relations  of  the  cerebellum  and  during  voluntary 
muscular  activity,  no  impulse  may  descend  from  the  brain  without 
an  influence  upon  its  direction  being  imparted  to  it,  both  in  its 
incipiency  as  a  result  of  the  cerebrally  afferent  impulses  from  the 
cerebellum  and  in  its  course  as  a  result  of  the  lower  indirect  efferent 
cerebellar  connections  with  the  lower  spinal  centers. 

The  cerebellarless  animal  shows  three  principal  symptoms  which 
are  all  referable  to  the  same  side  in  unilateral  ablations : 

1.  Asthenia  —  a  slight  loss  of  power  or  weakness. 

2.  Atonia  —  or  loss  of  tone ;  a  constant  undue  laxness  of  the 
muscles,  in  other  words. 

3.  Astasia  —  tremors  or  rhythmical  movements  of  the  muscles 
accompanying  every  willed  movement. 

All  these  three  symptoms  can  be  traced  to  the  failure  of  normal 
degree  of  responsiveness  of  the  muscles.  Each  contraction  starts 
in  a  more  relaxed  muscle  and  therefore  at  less  advantage,  and 
so  must  require  an  extra  voluntary  effort  to  accomplish  the  same 
end.  For  this  reason  there  is  apparent  weakness  of  the  muscles : — 
during  rest  an  undue  laxness  and  during  movement  a  frequent 
under  or  over  contraction,  which  results  in  tremors  and  inaccura- 

366 


THE  NERVOUS  SYSTEJNI 

cies  of  the  movement  to  the  desired  end.  This  inaccuracy  has 
its  origin  not  only  in  the  unpreparedness,  so  to  speak,  of  the 
muscles,  but  in  the  loss  of  the  organ  of  accurate  coordination. 

The  cerebellarless  animal  will  at  first  be  unable  to  stand  or 
walk,  but  after  several  months  may  again  be  able  to  walk.  The 
compensation  is  cerebral,  as  when  the  cerebrum  is  then  cut  off, 
permanent  paralysis  follows.  The  gait,  however,  of  such  a  cere- 
bellarless animal  is  characteristic.  There  is  a  constant  tendency, 
precisely  as  in  a  drunken  man,  for  the  center  of  gravity  to  fall  to 
one  or  the  other  side.  It  is  a  top-heavy  ataxia.  The  animal  is 
ever  ready  to  take  advantage  of  a  wall  against  which  it  may  lean 
during  its  progression.  In  order  to  correct  this  tendency  for  the 
center  of  gravity  to  fall  to  one  side  or  the  other,  it  makes  its  base 
of  support  as  wide  as  possible.  Each  diagonal  movements  starts 
with  less  advantages  and  is  accomplished  with  less  accuracy  than 
under  normal  condition. 

There  is  then  a  tendency  for  the  feet  to  move  too  little,  in 
order  to  place  the  center  of  gravity  in  a  correct  position  for  bal- 
ancing. This  tendency  must  be  corrected  by  an  extra  and  usually 
an  inaccurate  effort  on  the  part  of  the  cerebrum,  so  that  exces- 
sive movements  are  made  which  cause  the  animal  to  adopt  a  wide 
base  of  support  and  to  stagger. 

This  form  of  ataxia  is  called  cerebellar  ataxia. 

It  must  be  distinguished  from  two  other  forms  of  ataxia:  (1) 
spinal  or  tabetic  ataxia,  accompanying  lesions  in  the  posterior 
columns  of  the  cord,  and  (2)  ataxia  due  to  lesions  in  the  pyram- 
idal tracts. 

In  spinal  ataxia  the  movements  are  excessive  and  inaccurate  be- 
cause the  cerebrum  is  not  furnished  with  information  as  to  the  de- 
gree of  contraction  within  the  muscles.  It  consequently  can  only 
know  the  results  of  its  efforts  hy  the  use  of  the  eyes.  The  loss  of 
this  information  produces  the  impression,  so  to  speak,  on  the  cere- 
brum that  a  greater  degree  of  movement  is  required  than  the  cus- 
tomary amount  for  the  desired  end. 

In  addition,  therefore,  to  the  movements  being  inaccurate  they 
are  excessive.  The  cerebellar  and  vestibular  mechanism,  however, 
is  intact  and  so  there  is  not  that  loss  of  the  adjustment  of  move- 
ments of  the  body  as  a  whole  to  the  correct  position  of  the  center 
of  gravity  experienced  in  cerebellar  ataxia.    A  lesion  in  the  pos- 

368 


THE  NERVOUS  SYSTEM 

terior  columns  illustrates  defects  dependent  on  a  loss  of  one  kind  of 
function  presided  over  in  part  by  the  cerebellum. 

On  the  other  hand,  in  lateral  sclerosis,  in  which  condition  the 
lesion  is  in  the  pyramidal  tracts,  the  cerebrum  has  lost  the  main 
path  for  both  the  activation  and  control  of  the  motor  mechanism 
of  the  spinal  cord,  and,  in  consequence,  every  reflex  is  exaggerated. 

FUNCTIONS   OF   THE    CEREBRUM 

The  Contrast  between  the  Animal  Possessing  a  Cerebrum  and 
One  Without  a  Cerebrum  —  "When  we  investigate  the  functions  of 

the  cerebrum  we  at  once  are  struck  with  a  very  important  difference 
between  the  animal  possessing  a  cerebral  hemisphere  and  one  with- 
out one.  An  animal  deprived  of  its  cerebral  hemispheres  can  be 
played  upon  at  will ;  a  definite  response  will  always  follow  a  definite 
stimulus.  With  an  animal  possessing  a  cerebral  hemisphere  it  is 
impossible  to  foretell  just  what  response  will  follow  any  stimulus, 
[n  other  words  the  response  following  a  peripheral  stimulus  always 
is  incalculable.  Such  an  animal  is  influenced  by  many  feelings  in- 
volved in  the  action  of  its  consciousness.  Fear,  anger,  hunger,  affec- 
tion, will  all  cause  a  modification  of  stimulated  reflexes.  The  ques- 
tion suggests  itself,  and  did  long  ago  when  this  subject  was  first  con- 
sidered, are  certain  areas  in  the  cerebral  cortex  devoted  to  the 
exclusive  origination  of  these  various  impulses  or  feelings  which 
control  our  actions  ?  On  both  theoretical  and  experimental  grounds 
the  cerebral  cortex  cannot  be  thus  divided  into  areas  which  repre- 
sent the  various  predominating  states  which  characterize  our  con- 
sciousness. 

The  Foundation  of  all  Mental  Activity  upon  Association  of 
Ideas  (Association  of  Intracerebral  Groups  of  Impulses)  —  Abla- 
tion of  v£irious  portions  of  the  brain  does  not  remove  any  one  form 
of  activity  characterizing  our  intelligence,  but  rather  induces  a 
reduction  of  intelligence  as  a  whole.  The  whole  science  of  phrenol- 
ogy has  no  basis  in  fact.  On  the  o.ther  hand  certain  portions  of  the 
brain  are  intimately  associated  with  definite  forms  of  cerebral  activ- 
ity, but  only  with  those  forms  of  cerebral  activity  which,  if  we  may 
be  excused  for  using  the  term,  stand  immediately  next  to  the  out- 
side world  on  both  the  afferent  and  efferent  end  of  the  chain  of  links 
which  constitutes  perception,  judgment,  volition  and  finally  action. 

370 


THE  NERVOUS  SYSTEM 

The  afferent  and  efferent  end  of  this  chain  may  be  characterized  as 
perception  and  action. 

The  intervening  forms  of  cerebral  activity,  upon  which  judg- 
ment and  volition  are  based,  those  which  determine  what  action 
shall  follow  what  is  perceived,  call  into  activity  many  parts  of  the 
cerebral  cortex  and  are  only  possible  because  of  the  faculty  called 
memory.  But  what  is  memory  ?  Only  repetition  of  former  experi- 
ences within  the  mind,  the  actual  use  of  all  the  old  previously  well 
worn  cerebral  paths  used  in  former  experiences  minus  the  actual 
external  afferent  impulses  normally  associated  with  these  experi- 
ences. 

The  association  tracts  constitute  the  old  paths  and  the  old  ex- 
periences cannot  again  be  actuated  in  the  mind  without  the  use  by 
the  brain  of  all  the  association  tracts  in  the  brain  which  were  util- 
ized in  those  former  experiences,  and  by  again  bringing  into  rela- 
tion with  each  other  portions  of  the  brain  directly  connected  with 
perception  and  action,  though  these  portions  may  be  very  distant 
from  one  another.  And  so  it  is  that  all  the  brain  is  used  in  most 
of  our  intellectual  acts  and  states  of  consciousness. 

The  Localization  of  Function  in  the  Perceptive  and  Action  End 
of  the  Chain  of  Cerebral  Activities  —  All  in  the  above  paragraph 
is  very  far  from  meaning  that  no  portions  of  the  brain  are  definitely 
related  to  certain  forms  of  cerebral  activity.  It  is,  however,  only 
the  perception  and  action  end  of  the  chain  of  cerebral  events  which 
can  be  identified  with  special  areas  within  the  cerebral  cortex.  Let 
us  consider  first  the  areas  representing  action,  which  term  we  may 
select  to  describe  the  function  of  the  motor  areas.  The  motor  areas 
of  the  human  brain  are  all  within  the  ascending  frontal  convolution. 
From  above  downwards  are  centers  which  control  the  movements 
of  the  leg,  body,  arm  and  face.     (Figs.  145-147.) 

Stimulation  of  this  region  will  produce  coordinated  movements 
of  the  leg,  trunk,  arm  and  face.  In  the  dog  and  lower  animals  these 
areas  are  not  so  sharply  separated  as  they  are  in  the  higher  apes  or 
in  a  human  being.  Indeed  in  the  human  being  these  areas  are  even 
separated  by  unresponsive  spaces  or  partitions.  The  areas  may  be 
stimulated  by  weak  electrical  currents  directly  applied.  In  con- 
trast to  the  cerebellum  only  weak  currents  are  required,  even 
smaller  than  is  needed  to  stimulate  the  underlying  white  matter 
after  removal  of  the  gray  matter. 

372 


THE  NERVOUS  SYSTEM 


Anus  ^vA^ina.. 
,- ''Sulcus 


Abdomen 


Wriat 


Fin^ets 
\  thumb,. 


cords. 


Sulcus  centrdliS^ 


MasClcaCfon 


g.  145.— Brain  of  a  chimpanzee  (Troglodytes  niger).  Left  hemisphere  viewed  from  side 
and  above  so  as  to  obtain  as  far  as  possible  the  configuration  of  the  sulcus  centralis 
area. 

The  figure  involves,  nevertheless,  considerable  foreshortening  about  the  top  and  bottom 
sulcus  centralis.  The  extent  of  the  "motor"  area  on  the  free  surface  of  the  hemisphere 
indicated  by  the  black  stippling,  which  extends  back  to  the  sulcus  centralis.  Much  of 
e  "motor"  area  is  hidden  in  sulci;  for  instance,  the  area  extends  into  the  sulc.  centralis 
id  the  sulc.  precentrales,  also  into  occasional  sulci  which  cross  the  precentral  gyrus.  The 
imes  prmted  large  on  the  stippled  area  indicate  the  main  regions  of  the  "motor"  area, 
he  names  printed  small  outside  the  brain  indicate  broadly  by  their  pointing  lines  the  re- 
tion  topography  of  some  of  the  chief  subdivisions  of  the  main  regions  of  the  "motor" 
irtex.  But  there  exists  much  overlapping  of  the  areas  and  of  their  subdivisions  which 
e   diagram  does  not  attempt  to  indicate. 

The  shaded  regions,  marked  "EYES,"  indicate  in  the  frontal  and  occipital  regions  re- 
ectively  the  portions  of  cortex  which,  under  faradization,  yield  conjugate  movements  of 
e  eyeballs.  But  it  is  questionable  whether  these  reactions  sufficiently  resemble  those  of 
e  "motor"  area  to  be  included  with  them.  They  are  therefore  marked  in  vertical  shad- 
g  mstead  of  stippling,  as  is  the  "motor"  area.  S.F.,  superior  precentral  sulcus.  I.Pr., 
ferior  precentral  sulcus.     (Sherrington.) 


374 


THE  NERVOUS  SYSTEM 


This  fact  demonstrates  that  the  cerebral  cortex  itself  and  not  the 
underlying  white  matter  is  being  stimulated.  The  fact  is  further 
attested  to  by  the  absence  of  the  power  to  stimulate  the  cortex  after 


Stiiccatioso 

Sulc.parteCo 
occlp. 


Sulc.  Central,      "^"""j  *  ^'^^^* 

Sule.j>recenCr.  marg. 


Sulc.calcarin 


C.S.S.  dd. 


Left   hemisphere ; 


Fig.    146. — Brain    of   a    chimpanzee    (Troglodytes   niger). 

mesial  surface. 

The  extent  of  the  "motor"  area  on  the  free  surface  of  the  hemisphere  is 
indicated  by  the  black  stippling.  On  the  stippled  area  "LEG"  indicates  that 
movements  of  the  lower  limb  are  directly  represented  in  all  the  regions  of 
the  "motor"  area  visible  from  this  aspect.  Such  mutual  overlapping  of  the 
minuter  sub-divisions  exists  in  this  area  that  the  diagram  does  not  attempt 
to  exliibit  them.  The  pointing  line  from  "Anus,  etc.",  indicates  broadly  the 
position  of  the  area  whence  perineal  movements  are  primarily  elicitable. 

Sulc.  central,  central  fissure;  Sulc.  calcarin.,  calcarine  fissure;  Sulc.  parieto 
occip.,  parieto-occipital  fissure;  Sulc.  calloso  marg.,  calloso-marginal  fissure; 
Sulc.  precentr.  marg.,  pre-central  fissure. 

The  single  italic  letters  mark  spots  whence,  occasionally  and  irregularly, 
movements  of  the  foot  and  leg  (ff),  of  the  shoulder  and  chest  (s)  and  of  the 
thumb  and  fingers  (/i)  have  been  evoked  by  strong  faradization.  Similarly 
the  shaded  area  marked  "EYES"  indicates  a  field  of  free  surface  of  cortex 
which  under  faradization  yields  conjugate  movements  of  the  eyeballs.  The 
conditions  of  obtainment  of  these  reactions  separates  them  from  those  char- 
acterizing the  "motor"  area.     (Sherrington.) 

it  has  been  painted  with  cocaine  or  after  the  administration  of 
chloral.  ]\Ioreover  the  latent  period  after  stimulating  the  gray 
matter  is  longer  (.065  second)  than  when  the  white  matter  is  di- 
rectly stimulated  (.045  second). 

376 


THE  NERVOUS  SYSTEM 


Characteristics  of  Movements  Excited  in  the  Cerebrum  —  By 

stimulation  of  the  cortex  coordinated  movements,  precisely  similar 
to  normal  voluntary  movements  are  elicited.  This  fact,  of  course, 
means  that  the  normal  tone  of  some  muscles  must  be  inhibited.  This 
inhibition  is  absent  during  strychnine  and  tetanus  poisoning  so  that 

Prontel 

association 

area 


Parietal 
*^  association 
area 


Temporo-cccipital 
association  area 


Parietal 
.association 
area    \ 


Frontal 
-association 
area 


Temporo-cccipital 
association  area 

Fig.  147. — Diagrams  suggesting  the  general  motor,  general  and  special  sensory 

and  the  association  areas  of  the  convex  and  mesial  surfaces 

of  the  cerebral  hemisphere.     (Morris.) 

under  the  influence  of  these  drugs  only  movements  are  obtained 
which  represent  those  of  the  stronger  set  of  muscles. 

The  part  played  by  inhibition  is  well  illustrated  by  the  eye 
movements.  When  the  convex  surface  of  the  inferior  frontal  con- 
volution on  the  right  side  is  stimulated  both  eyes  turn  toward  the 

378 


THE  NERVOUS  SYSTEM 

left.  This  movement  can  only  take  place  in  the  right  eye  by  a 
simultaneous  relaxation  of  the  right  external  rectus  and  contraction 
of  the  right  internal  rectus  and  the  reverse  of  these  events  in  the 
left  eye.  After  division  of  all  the  muscles  of  the  right  eye  except 
the  external  rectus  the  eye  will  be  constantly  turned  outward.  The 
same  stimulus  applied  now  will  cause  a  sufficient  relaxation  of  the 
right  external  rectus  to  permit  of  the  eye  returning  to  the  middle 
line. 

These  eye  movements  further  illustrate  the  bilateral  effect  of 
certain  unilateral  cortical  stimulation.  In  other  words  they  illus- 
trate that  every  movement  originating  in  the  cortex  is  a  purpose 
movement. 

The  Contrast  and  Interaction  between  the  Control  over  Move- 
ment Exerted  by  the  Cerebrum  and  Cerebellum  —  The  cerebellum 
also  plays  an  important  part  in  this  same  control.  Both  organs 
participate  in  the  maintenance  of  muscular  tone  and  both  are  able 
to  do  so  by  inhibition;  but  it  is  the  special  function  of  the  cere- 
bellum to  maintain  that  constant  tone  which  is  essential  to  attitude 
while  the  cerebrum  is  responsible  for  changing  activity. 

The  cerebellum  may  be  spoken  of  as  the  automatic  agent  of  the 
brain  in  the  influence  which  it  exerts  in  response  to  sensory  im- 
pulses, while  the  cerebrum  is  the  voluntary  agent;  the  cerebellum 
is  the  special  center  for  continuous  muscular  contraction,  while  the 
cerebrum  is  the  center  for  changing  movements  and  may  be  played 
upon  by  other  afferent  impulses  leading  to  voluntary  contraction  as 
well  as  by  impulses  through  the  proprioceptive  system.  The  cere- 
bellum may  be  viewed  as  a  special  receiving  organ  for  propriocep- 
tive impulses,  where  these  impulses  find  a  mechanism  capable  of 
passing  on  to  the  rest  of  the  central  nervous  system  impulses,  re- 
sulting in  equilibrium  and  normal  muscular  tone.  To  a  large 
degree  these  efferent  impulses  from  the  cerebellum  pass  through  the 
cerebrum  which  in  turn  uses  the  cerebellar  mechanism,  as  a  pre- 
pared, accurately  adjusted  and  sensitive  mechanism  for  the  produc- 
tion of  an  automatic  unconscious  coordination.  The  cerebrum  gives 
direction  to  this  coordination  in  the  voluntary  changes  of  activity 
for  which  it  alone  is  responsible. 

The  Difference  in  the  Functions  of  the  Cerebral  Motor  Areas  in 
Man  and  in  the  Animal  —  Effects  of  removal  of  the  motor  centers 
are  very  different  in  man  and  in  animals  even  so  high  in  the  scale 

380 


THE  NERVOUS  SYSTEM 

of  life  as  the  dog.  In  the  dog  the  first  effect  of  the  removal  of  the 
motor  area  is  a  very  severe  disturbance  of  the  dog's  power  of  move- 
ment. The  muscles  on  the  side  opposite  to  the  operation  are  much 
weaker.  Recovery  takes  place  after  a  few  weeks,  such  complete 
recovery  that  the  animal  can  be  taught  new  movements  involving 
the  use  of  the  affected  limb. 

In  the  monkey  recovery  is  less  complete.  There  is  some  perma- 
nent awkwardness  and  the  immediate  effect  is  one  of  absolute  par- 
alysis. 

In  man  lesions  of  the  motor  area  produce  still  more  serious 
effects.  There  is  absolute  paralysis  at  first  and  only  a  very  trivial 
amount  of  recovery,  if  the  pathological  condition  can  be  removed. 
The  amount  of  recovery  will  be  inversely  proportional  to  the 
amount  of  the  motor  area  destroyed  by  the  lesion  or  its  operative 
removal. 

These  graded  consequences  of  destruction  of  the  motor  area 
among  animals  and  man  are  another  illustration  of  the  shifting  of 
nervous  activities  as  we  ascend  the  scale  of  life  from  that  region 
where  they  are  necessitated  by  direct  paths  and  few  association 
tracts,  activities  that  may  be  characterized  by  the  word  fateful,  to  a 
region  where  they  are  conditioned  by  any  one  set  of  a  host  of  affer- 
ent impulses  reaching  the  regions  in  question  along  any  set  of 
numerous  association  tracts  which  all  together  make  consciousness 
possible. 

In  man  there  exists  the  possibility  of  a  greater  variation  in 
response,  or,  in  other  language,  a  greater  variety  of  movements. 
Actions  become  based  on  motive  and  new  cerebral  activities  impos- 
sible in  the  animal  are  learned. 

In  man  all  must  be  learned  at  the  expense  of  education.  Man 
comes  into  the  world  with  comparatively  few  laid  down  paths.  For 
many  years,  as  a  reactive  organism,  he  is  far  inferior  to  the  lower 
animals.  It  is,  however,  only  in  virtue  of  this  fact  that  in  him  a 
greater  adaptation  of  action  to  intelligent  needs  becomes  possible. 

The  Dependence  of  the  Motor  Area  upon  Different  Impulses  to 
it  —  In  speaking  of  the  motor  area  as  a  center  for  voluntary  im- 
pulses we  must  not  consider  that  the  whole  chain  of  events  leading 
to  a  movement  occurs  in  the  motor  area,  or  that  all  movements  arise 
there.  Like  the  cells  in  the  anterior  horns  of  the  spinal  cord  the 
cells  of  the  motor  area  are  utilized  as  the  last  chain  in  a  series  of 

382 


THE  NERVOUS  SYSTEM 

cerebral  events  and  are  played  upon  by  other  impulses  partici- 
pating in  the  complex  mechanism  which  alone  makes  possible  choice 
of  action. 

The  Receiving  End  of  the  Mechanism  —  Having  discussed  the 
motor  or  discharging  mechanism,  let  us  turn  to  the  other  end  of  the 
chain  of  cerebral  events,  the  receiving  mechanism.  Of  first  im- 
portance is  that  region  of  the  brain  which  is  most  closely  related 
to  the  perception  of  tactile  and  muscular  sensibility.  Many  facts 
indicate  that   the   ascending  parietal  convolution  is   the   seat   of 

'TactiuE.'  area 


VkSUAU 


Auditor.  V    /\Re~f\ 


Fig.  148. — Outline  drawing  of  the  external  surface  of  the  hemisphere.    Shaded 

portion  represents  the  receptive  area  for  tactile, 

auditory  and  visual  sensations. 

the  direct  perception  of  tactile  and  muscular  sensibility.     (Figs. 
148  to  149.) 

(1)  "Widespread  lesions  in  the  motor  area  will  not  only  produce 
piaralysis  but  more  or  less  complete  hemi-anesthesia. 

(2)  Lesions  posterior  to  the  fissure  of  Rolando  including  the 
posterior  central  convolution,  the  superior  and  inferior  parietal, 
and  the  supramarginal  convolutions  are  characterized  by  more  pure 
disturbances  of  sensation. 

(3)  In  the  same  manner  certain  more  posterior  lesions  of  this 
and  the  motor  area  of  the  brain,  causing  Jacksonian  epilepsy,  may 
be  preceded  by  sensory  aura.  The  sensory  areas  are  less  definitely 
located  than  the  motor  areas  and  may  overlap  and  in  part  invade 

384 


THE  NERVOUS  SYSTEM 

the  motor  area.  The  sensory  perceptions  located  in  this  region  of 
the  brain  include  the  sense  of  pressure,  of  temperature  and  the 
muscular  sense  that  is  all  sensations  involved  in  stereognostic  per- 
ception. The  sense  of  pain  is  not  included  in  this  perception.  It 
includes  only  those  single  perceptions  which  are  needed  for  the 
perception  of  form,  size  and  solidity.  Lesions  in  region  mentioned 
cause  chiefly  a  disturbance  of  stereognostic  perception,  a  symptom 
named  astereognosis.  With  these  lesions  the  sense  of  pain  is  little 
if  at  all  affected.  Even  in  tabes  dorsalis  there  is  atrophy  of  the 
posterior  central  convolution. 

Tactile.*    area 


OUFACTOR-Y     AR.E.A 

Fig.  149. — Inner  surface  of  the  same  hemisphere. 

The  impulses  of  these  sensations  ascend  in  the  mesial  fillet  to 
the  optic  thalamus  and  pass  thence  by  a  new  set  of  fibers  through 
the  hinder  limb  of  the  internal  capsule  to  the  parietal  region. 

The  thalamus,  however,  sends  fibers  to  other  portions  of  the 
brain.  Cortical  lesions  of  the  central  convolutions  never  produce 
complete  hemianesthesia,  so  that  while  the  posterior  central  or 
ascending  parietal  convolution  is  the  chief  cerebral  receiving  station 
for  tactile  and  muscular  sensations,  widely  separated  otlier  portions 
of  the  brain  may  participate  in  this  function. 

Visual  Perception  - —  This  is  located  in  the  occipital  lobe,  in  the 
euneus  and  convolutions  bordering  the  calcarine  fissure.  Very  defi- 
nite evidence  exists  in  support  of  this  fact. 

386 


THE  NERVOUS  SYSTEM 

(1)  Excision  of  one  occipital  lobe  causes  crossed  hemianopsia, 
i.e.,  blindness  in  the  half  of  each  retina  which  is  opposite  to  that 
of  the  extirpated  lobe.  This  bilateral  effect  is  explained  by  the 
manner  in  which  the  optic  fibers  cross  in  the  optic  chiasma. 

(2)  Stimulation  of  the  occipital  lobe  in  an  animal  causes  the 
eyes  to  move  toward  the  opposite  side  because  of  a  revival  of  past 
visual  sensations. 

(3)  The  eyes  will  move  downward  and  to  the  opposite  side  if 
the  upper  part  of  the  occipital  lobe  is  stimulated  and  upward  and 
to  the  opposite  side  if  the  lower  portion  of  occipital  lobe  is  stim- 
ulated. 

(4)  From  the  hinder  end  of  the  pulvinar  and  external  genicu- 
late body  which  receive  the  optic  nerves,  fibers  arise  which  pass 
through  the  hinder  end  of  the  internal  capsule  and,  as  the  optic 
radiations,  to  occipital  lobes. 

(5)  Pathological  lesions  fully  confirm  these  conclusions. 
Perception  of  hearing"  —  Situated  in  the  superior  temporal  con- 
volution; but  probably  not  entirely  here. 

(1)  Extirpation  of  the  superior  temporal  convolution  in  mon- 
keys produces  marked  disturbances,  but  not  a  complete  disturbance 
of  hearing. 

(2)  Cortical  lesions  of  the  superior  temporal  convolution  in  man 
produce  varying  degrees  of  deafness. 

(3)  Stimulation  of  the  superior  temporal  convolutions  will 
cause  animals  to  prick  up  their  ears  as  if  sounds  were  heard. 

(4)  From  the  auditory  nucleus  in  the  medulla  nerve  fibers  pass 
to  the  trapezium,  and  thence  by  the  lateral  fillet  to  the  inferior  cor- 
pora quadrigemina.  From  this  body  and  the  internal  geniculate 
body  they  pass  into  the  hinder  parts  of  the  internal  capsule  and 
thence  as  the  auditory  radiations  to  the  superior  temporal  convolu- 
tions. The  fibers  from  the  two  internal  geniculate  bodies  decussate 
across  the  middle  line  in  Guddens'  commissure  which  form  the  pos- 
terior fibers  of  the  optic  chiasma. 

Smell  and  Taste  Perception  is  located  in  the  hippocampal  gyrus, 
the  dentate  convolution  and  in  that  portion  of  the  limbic  lobe  known 
as  the  gyrus  fornicatus  which  immediately  borders  the  superior 
surface  of  the  corpus  callosum.  Among  animals  the  sense  of  smell 
is  a  far  more  important  sense  than  in  man.  Its  connections  are, 
therefore,  widespread.    In  man  it  is  only  natural  to  expect  that  the 

388 


THE  NERVOUS  SYSTEM 


-same  widespread  connections  should  exist  and,  perhaps,  be  all  the 
less  well  defined  on  account  of  the  contemporaneous  huge  develop- 
ment of  the  rest  of  the  brain  and  the  corresponding  disappearance 
of  the  acuteness  of  the  perception  of  smell  (see  Fig.  147). 

Electrical    stimulation    of    the    hippocampal    convolution    has 
caused  movements  of  the  lips  and  nostrils.    Ablation  experiments 

Broca  area  third  inf.  frontal 
''     co-ordination  of  speech  muscles. 

Ascending  parietal  convol.  motor 
/        area  for  hand  graphic  images. 

Ascending  parietal 
motor  area  for 
mouth  and  larynx. 

Supramarginal 
convol. 
auditory 
word  images. 


Visual 
area 
cuneus. 


Sup.   temp,   convol. 
auditory  area. 


Mid.    temp,    convolution 
word     understanding. 


Fig.    150. — Convex    surface    of    left    cerebral    hemisphere    and    diagrammatic 
presentation  of  the  areas  suggested  as  concerned  with  speech.     (Morris.) 

have  not  given  much  information.  The  most  valuable  information 
is  to  be  derived  from  the  connections  in  the  lower  animals.  In  addi- 
tion to  the  portions  of  the  brain  which  we  have  mentioned,  the  pos- 
terior part  of  the  inferior  surface  of  the  frontal  lobe  and  the  olfac- 
tory lobe  and  the  anterior  commissure  must  be  included. 

Association  Areas  and  the  Significance  of  Association  of  Cere- 
bral Impulses  and  Their  Relation  to  Thought  and  Speech  —  The 
areas  of  the  brain  which  we  have  identified  with  perception  and 
action  occupy  a  comparatively  small  amount  of  the  cortex  of  the 
brain. 

390 


THE  NERVOUS  SYSTEM 

Inasmuch  as  the  cerebral  processes  transpiring  within  these 
areas  cannot  be  unraveled,  they  have  been  termed  the  silent  areas, 
and  as  the  living  being  rises  in  the  scale  of  intelligence  these  areas 
become  relatively  larger.  They  make  up  by  far  the  larger  portion 
of  man's  brain. 

AA-'hen  we  attempt  to  analyze  the  cerebral  processes  accompany- 
ing a  single  combination  of  sensations  and  the  infinite  variety  of 
cerebral  processes  representing  the  result  of  the  influence  of  these 
sensations  collectively,  it  is  quite  evident  that  even  simple  forms  of 
cerebral  activity  are  very  intricate.  Thinking  is  only  possible 
because  of  man 's  power  to  quickly  call  into  use,  or  in  other  words 
to  associate,  many  portions  of  the  brain  which  have  to  do  with  pre- 
vious sensations.  So  intricate  does  this  activity  become  that  a  large 
part  of  the  advantage  of  the  means  for  this  association  becomes  lost 
without  provision  for  cerebral  short  cuts.  The  association  itself  is 
primarily  accomplished  by  connecting  neurons  and  the  process  of 
association  of  impulses  or  a  set  of  impulses  which  have  been  linked 
together  as  a  unit  (such  a  unit  often  constituting  a  concept  or  idea) 
is  facilitated  by  the  laying  down  of  other  fibers  or  even  tracts  which 
furnish  short  cuts  and  which  make  possible  the  more  rapid  revival 
of  not  only  past  perceptions  as  they  happen  to  be  related  to  a  par- 
ticular stimulus  starting  the  cerebral  activity,  but  also  whole  groups 
of  perceptions,  taken  as  a  whole. 

The  Grouping  of  Perception  Made  Possible  by  Speech  —  These 
short  cuts,  therefore,  make  possible  education  and  memory. 

Speech  —  In  the  development  of  man  the  rapid  association  of 
groups  of  impulses  constituting  concepts  has  been  greatly  facili- 
tated by  the  adoption  of  audible  symbols  for  concepts.  By  this 
invention  man  has  rendered  possible,  as  a  result  of  his  greater  power 
of  association  and  his  power  of  phonation,  an  almost  indefinite 
enlargement  of  the  power  of  reviving  instantaneously  past  associa- 
tions of  great  complexity.  Upon  this  invention  alone  depends  our 
power  of  intricate  thinking. 

The  Varieties  of  Aphasia  —  Various  disturbances  of  the  power 
of  speech  demonstrate  more  closely  the  cerebral  processes  upon 
which  it  is  based.  A  number  of  different  forms  of  aphasia  have 
been  described. 

(1)  Motor  Aphasia  —  This  form  of  aphasia  has  been  described 
as  an  inability  to  speak  though  the  individual  understands  every- 

392 


THE  NERVOUS  SYSTEM 

thing  which  is  said  to  him  and  suffers  no  impairment  of  his  intelli- 
gence. This  form  of  aphasia  has  been  for  a  long  time  associated 
with  a  lesion  in  the  third  left  frontal  convolution  immediately  an- 
terior to  the  lower  end  of  the  ascending  frontal  convolution.  This 
area  has  been  called  Broca  's  area,  after  the  man  who  first  described 
the  aphasia  and  its  associated  lesion.  The  traditional  association  of 
motor  aphasia  with  a  lesion  in  the  third  left  (right-handed  people) 
convolution  has  been  so  strong  that  few  clinicians  do  not  accept  it 
outright.  Nevertheless  the  association  will  not  bear  investigation. 
Theoretically  it  should  not.  The  complex  character  of  all  the  asso- 
ciations necessary  to  speech  cannot  be  grouped  in  one  center  of  the 
brain,  and  the  same  argument  contradicts  with  equal  force  the  too 
strict  localization  of  sensory  aphasia  with  the  area  of  Wernicke. 

Undoubtedly  near  Broca 's  area  in  the  cortex  are  the  motor  cen- 
ters for  the  muscles  of  the  larynx,  but  the  majority  of  eases  of  motor 
aphasia  are  really  a  species  of  anarthria,  and  upon  autopsy  are 
found  to  be  associated  with  lesions  in  other  locations  particularly 
in  the  external  capsule  and  the  anterior  portion  of  the  internal 
capsule.  No  good  ground  exists  for  distinguishing  between  motor 
aphasia,  when  intelligence  is  unimpaired,  and  the  type  of  aphasia 
described  below  by  the  word  anarthria.  The  majority  of  cases  de- 
scribed as  motor  aphasia  are  associated  with  impaired  intelligence 
and  belong  in  the  second  variety  of  aphasia. 

(2)  Sensory  Aphasia  or  Aphasia  of  Wernicke  —  This  form  of 
aphasia  is  associated  with  lesions  in  the  supra-marginal  and  angular 
gyri  and  posterior  end  of  the  second  temporal  convolutions.  In  this 
condition  there  may  be  limited  power  of  speech,  but  there  is  impair- 
ment of  intelligence  and  especially  of  the  appreciation  of  spoken 
words.  There  may  also  be  loss  of  power  to  recognize  written  words 
(alexia).  The  motor  portion  of  this  aphasia  is  due  rather  to  the 
individual's  inability  to  understand  his  own  spoken  words. 

(3)  Anarthria  —  In  this  condition  there  is  a  pure  impairment 
of  the  motor  powers  of  expression.  It  is  generally  associated  with 
a  lesion  in  the  external  capsule.  Appreciation  of  speech  written 
and  spoken  is  perfect  and  intelligence  is  unaltered. 

Wernicke 's  area  must  be  regarded  as  only  one  of  the  great  asso- 
ciation centers  of  the  brain  between  various  forms  of  perception  and 
between  them  and  motion.  Lesions  in  them  mean  a  blunting  of 
intelligence,  because  the  power  of  forming  complete  concepts  is 

394 


THE  NERVOUS  SYSTEM 

lacking  though  the  individual  may  be  in  perfect  possession  of  the 
logical  faculty.  In  true  insanity  there  is  an  impairment  of  the 
higher  association  centers  located  in  the  prefrontal  region.  The 
simpler  concepts  are  perfectly  formed  hut  the  power  of  grouping 
these  in  a  manner  necessary  for  the  processes  involved  in  logical 
thought  is  lost.  By  means  of  the  myelinization  method  Flechsig  has 
been  able  to  divide  up  the  cerebral  cortex  into  some  36  areas.  Eight 
of  these  belong  to  the  regions  which  have  been  described  as  asso- 
ciated with  the  action  end  or  primary  projection  areas  of  the  cor- 
tex. 

In  the  case  of  seven  areas  the  function  is  uncertain.  The  areas 
do  not  possess  either  projection  fibers  or  apparently  association 
fibers. 

Eighteen  areas  are  provided  with  short  association  fibers.  They 
may  be  termed  intermediate  areas. 

Three  areas  possess  long  association  fibers.  They  may  be  termed 
the  large  and  important  association  areas.  One  of  these  occupies 
the  prefrontal  region  on  both  the  internal  and  external  surface  of 
the  cortex.  A  second  occupies  the  2nd  and  3rd  temporal  convolu- 
tions and  the  third  a  large  area  on  the  external  surface  of  the  cor- 
tex, including  the  posterior  portion  of  the  supramarginal  convolu- 
tion and  extending  posteriorly  to  the  visual  perception  area  in  the 
cuneus.  Until  comparatively  recently  the  nuclei  of  gray  matter 
grouped  under  the  name  of  the  corpus  striatum  and  including  the 
lenticular  nucleus  and  the  caudate  nucleus  were  regarded  as  simi- 
lar in  function  to  the  optic  thalamus  and  like  it  to  constitute  merely 
relay  stations  for  impulses  on  the  way  to  and  from  the  brain. 
After  destroying  these  nuclei,  however,  degenerated  fibers  are 
found  passing  from  them  to  the  optic  thalamus.  These  nuclei, 
therefore,  send  out  efferent  fibers  to  lower  cerebral  nuclei.  They 
are  also  known  to  receive  fibers  from  the  optic  thalamus  and  the 
olfactory  tracts.  Such  connections  indicate  that  these  nuclei 
are  independent  masses  of  gray  matter  capable  of  receiving  afferent 
impulses  from  below  and  of  sending  out  independent  efferent  im- 
pulses. They  must  be  regarded  as  relay  stations  within  the  brain 
itself  between  the  cortex  and  the  lower  thalamic  centers. 

In  a  series  of  animals  representing  an  ascending  scale  of  cere- 
bral development  the  corpus  striatum  occupies  a  relatively  less 
importance  in  cerebral  activities.    In  birds,  on  the  other  hand,  they 

396 


THE  NERVOUS  SYSTEM 

have  their  greatest  development.  It  would  appear  that  they  repre- 
sent then  a  divergent  development  in  birds,  taking  over  an  in- 
creasing number  of  functions  in  them,  while  in  mammals  they  are 
retrogressive,  their  functions  being  shifted  to  the  pallidium  or 
cerebral  hemispheres.     Stimulation  of  these  nuclei  produces  no 


Grenu  of  corpus  callosum. 
Anterior     horn     of     lateral 
ventricle. 

Caudate  nucleus. 
Anterior    limb     of     Internal 
capsule. 

Cavum    septl    pellucidi. 

Gtenu  of   internal   capsule. 

Column   of  fornix. 

Globus    pallldus    (of   nucleus 

lentiformis). 
Fasciculus       mammillothala- 

mlcus. 
■Posterior     limb    of    internal 
capsule.  „    , 

Thalamus. 
Retrolenticular    part    of    in- 
ternal capsule. 

Hippocampus. 

Splenium. 

Chorioid    plexus. 

Gyrus   cinguli. 

Calcarine    sulcus. 


Lenticulo-caudate  fibres. 
Claustrum. 


nucleus      lentifor- 


Intemal    capsule    with    ansa 
lenticularis   fibres   in  blue. 


Tail    of   caudate   nucleus. 

Optic    radiation. 
Tapetum. 

Optic  radiation  passing  back 
to  white  line  in  the  area 
striata. 


Fig.  151. — Horizontal  section  through  the  right  cerebral  hemisphere  at  the 
level  of  the  widest  part  of  the  lentiform  nucleus.      (Cunningham.) 


movements.  In  the  monkey  their  destruction  is  followed  by  no 
definite  results.  In  man  lesions  in  these  bodies  produce  tremors 
in  the  execution  of  willed  movements  and  an  increased  tonicity  of 
the  muscles,  functions  resembling  those  of  the  cerebellum. 

Experimental  evidence  of  the  nature  of  the  application  of  iso- 
lated heat  and  cold  to  the  anterior  part  of  the  corpus  striatum  indi- 
cates that  this  portion  of  gray  matter  contains  the  chief  thermo- 

398 


THE  NERVOUS  SYSTEM 


taxic  center  of  the  body.  Cooling  it,  for  instance,  produces  shiver- 
ing and  increased  lieat  production  in  the  body,  while  warming  it 
produces  the  opposite  effect. 

The  Histological  Structure  of  the  Cortex  —  The  preceding  lo- 
calization of  nervous  function  within  the  cerebral  cortex  is  largely 
confirmed  by  a  study  of  the  histological  structure  of  the  cortex.  The 
cortex  consists  of  many  layers  of  cells  imbedded  in  a  neuroglia  sup- 
porting framework.  As  the 
pi.oiExMT  p^p]jjj2je  cells  are  characteris- 
tic of  the  cerebellum,  so  the 
pyramidal  cell  belongs  pecu- 
^'"^"'''"''liariy  to  the  cerebral  cortex. 
It  is  a  cone-shaped  or 
pear-shaped  cell  with  one 
large  apical  dendrite  which 
runs  towards  the  surface  to 
break  up  in  the  most  super- 
ficial layers  of  the  cortex  into 
o/Ba.7(  a  number  of  branches.  Den- 
drites are  given  off  from  the 
sides  of  the  cell.  The  axon 
;»„,  starts  in  the  base  of  the  cell 
and  passes  down  into  the 
white  matter,  giving  off  col- 
""''     laterals  in  its  course. 

Some  fibers  reach  the  cor- 
pus callosum,  others  the  in- 
ternal capsule,  and  others  ad- 
jacent parts  of  the  cortex. 
<:v,h.>  There  may  be  distin- 
guished four  or  five  layers  of 
cells  within  the  cortex.  (Fig. 
152.)  (1)  Outer  fiber  lamina 
or  molecular  layer  contains 
few  cells  spindle-shaped  the 
processes  of  which  run  paral- 
lel to  the  surface.  The  layer 
is  mostly  composed  of  the 
branching    dendrites    of    the 


Fig.  152. — Cerebral  cortex,  diagrammatic 
section. 
On  the  left,  the  cellular  layers;  on  the 
right,  systems  of  fibres;  on  the  extreme 
left  a  sensory  fibre  is  seen  ascending; 
1,  2,  3,  4,  the  four  layers  of  cells;  2  and  3 
representing  pyramidal  cells  of  differing 
size. 


400 


THE  NERVOUS  SYSTEM 

cells  of  tlie  deeper  layers.  (2)  Outer  cell  lamina  or  pyramidal 
cell  layer. 

It  contains  three  varieties  of  pyramidal  cells  arranged  from 
without  inwards  into  (a)  small  pyramidal  cells,  (b)  medium  pyra- 
midal cells,  (c)  large  pyramidal  cells.  (3)  Stellate  cell  layer  or 
middle  cell  lamina,  as  indicated,  contains  stellate-shaped  cells.  (4) 
Inner  fiber  lamina,  composed  of  many  nerve  fibers  and  in  certain 
portions  of  the  brain,  particularly  the  motor  areas,  this  layer  con- 
tains large  solitary  cells,  the  cells  of  Betz.  (5)  The  polymorphous 
cell  layer  and  inner  cell  lamina,  containing  cells  of  many  types,  but 
among  which  the  pyramidal  cells  predominate.  Some  of  the  pyra- 
midal cells  are  inverted,  so  to  speak,  their  axons  run  to  the  surface. 
These  are  called  cells  of  Marinotti.  Other  cells,  Golgi  cells,  possess 
freely-branching  axons  ending  near  the  cell. 

The  fibers  from  the  white  matter  of  the  brain  run  toward  the 
surface,  giving  off  a  rich  meshwork  of  fibers  to  the  various  layers 
of  gray  matter.  Other  fibers  run  parallel  to  the  surface  and  on  the 
very  surface  of  the  brain.  These  fibers,  in  some  regions,  especially 
the  hippoeampal  region,  are  so  well  marked  that  they  are  termed 
the  tangential  fibers. 

Another  layer  of  tangential  fibers  is  found  between  the  molecu- 
lar layer  and  the  pyramidal  cell  layer.  It  is  called  the  outer  line  of 
Baillance. 

Internal  to  the  granular  layer  is  another  layer  of  tangential 
fibers,  the  inner  line  of  Baillance. 

In  the  occipital  region  there  is  a  special  tangential  layer  running 
through  the  middle  of  the  granular  layer.  It  is  called  the  line  of 
Gennari. 

Identification  of  Function  iy  Means  of  Histological  Detadl  — 
The  thickness  of  these  various  layers  furnish  information  as  to  the 
function  of  the  various  portions  of  the  cerebral  cortex. 

In  the  ascending  frontal  convolution  the  cells  of  Betz  are  numer- 
ous and  larger  than  in  any  other  region.  The  pyramidal  cell  layer 
is  also  very  thick. 

In  the  visuo-sensory  area  the  stellate  cell  layer  or  granular  layer 
is  thickest  and  the  line  of  Gennari  present. 

In  association  areas,  the  parietal,  temporal  and  frontal  the  outer 
cell  layer  or  pyramidal  cell  layer  is  very  thick.     It  is  the  most 

402 


THE  NERVOUS  SYSTEM 

marked  feature  of  sections  in  these  regions.  These  cells,  therefore, 
have  to  do  with  the  higher  functions  of  association. 

In  animals  lower  than  man,  the  ape  and  dog,  less  of  the  brain  is 
occupied  with  areas  possessing  the  histological  structure  identified 
with  association.  In  still  lower  animals,  the  rabbit,  the  polymor- 
phous layer  is  three  times  the  thickness  of  the  pyramidal  layer. 

"We  may,  therefore,  assign  to  the  cells  of  Betz  motor  function,  to 
the  pyramidal  cells  associative  functions,  and  to  the  polymorphous 
cells  functions  concerned  in  the  getting  of  food  and  the  gratification 
of  the  various  sensuous  instincts. 

"When  the  cerebral  activities  are  deficient  either  because  of  dis- 
ease or  congenital  defects,  the  cells  are  less  numerous  in  the  regions 
controlling  the  deficient  functions. 

Time  of  Certain  Cerebral  Activities  —  The  time  of  the  various 
seactions  in  which  the  brain  is  concerned  is  of  interest.  They  may 
be  recorded  by  an  electrical  apparatus  which  marks  the  moment  of 
the  application  of  any  stimulus  and,  through  a  shunt  circuit,  the 
voluntary  reaction  of  the  patient. 

The  time  for  the  reaction  to  sight  stimuli  is  .186  to  .222  of  a 
second;  to  hearing  .115  to  .182  second;  to  electrical  stimulation  of 
skin  .117  to  .201  second. 

The  time  may  be  lengthened  .006  second  by  fatigue  of  the  reac- 
tion, or  by  a  dilemma,  involving  choice  by  the  individual. 

It  may  be  shortened  by  practice,  or  by  increase  in  strength  of 
the  stimulus. 


THE    SYMPATHETIC    NERVOUS   SYSTEM 

The  nerves  passing  from  the  central  nervous  system  to  the  vari- 
ous portions  of  the  body  may  be  divided  into  two  different  classes. 
First  those  conveying  motor  impulses  from  the  spinal  cord  and 
brain  and  those  returning  sensory  impulses.  In  addition  to  these 
nerves  there  is  another  class  of  nerves  issuing  with  the  cranial 
nerves  and  the  anterior  and  posterior  roots  of  the  spinal  nerves 
which  convey  afferent  impulses  from  and  efferent  impulses  to  the 
blood  vessels  and  viscera. 

Briefiy,  they  supply  smooth  muscle  and  glandular  tissue. 

The  nerves  of  this  second  class  are  connected  with  peripheral 

404 


THE  NERVOUS  SYSTEM 

ganglia  and  differ  histologically  from  other  nerved.  All  these  facts 
warrant  their  classification  as  a  separate  system. 

It  is  called  the  vegetative  nervous  system,  and  may  be  divided 
into  the  autonomic  or  cranial  portion  of  the  vegetative  nervous 
system  and  the  spinal  portion  or  the  sympathetic  nervous  system. 

In  contradistinction  from  it  we  may  call  the  other  nerves  of  the 
body  those  innervating  skeletal  muscle  and  returning  sensory  im- 
pulses the  somatic  nervous  system. 

The  vegetative  nerves  of  the  third  cranial  nerve  pass  with  the 
third  nerve  to  the  orbit.  Leaving  the  branch  of  the  third  nerve 
which  supplies  the  inferior  oblique  muscle,  they  enter  the  lenticular 
ganglion.  From  this  ganglion  their  axons  are  continued,  after  inter- 
ruption, as  the  short  ciliary  nerves  to  the  sphincter  pupili  muscle 
and  the  ciliary  muscles. 

The  vegetative  nerves  of  the  7th  cranial  nerve  are  contained  in 
the  nerve  of  Wrisberg.  This  nerve  also  contains  fibers  of  taste  from 
the  tongue.  The  fibers  belonging  to  the  vegetative  system,  however, 
leave  the  7th  nerve  as  the  chorda  tympani  and  later  join  the  lingual 
nerve  and  with  this  pass  to  the  submaxillary  ganglion.  From  this 
ganglion  it  supplies  dilator  fibers  and  secretory  fibers  to  the  sub- 
maxillary and  sublingual  salivary  glands.  The  chorda  tympani 
also  sends  fibers  to  the. sphenopalatine  ganglion  from  which  post- 
ganglionic fibers  supply  the  mucous  membrane  of  the  nose  and  soft 
palate  and  upper  part  of  the  pharynx. 

The  vegetative  fibers  of  the  9th  nerve  pass  to  the  otic  ganglion. 
From  this  ganglion  its  post  ganglionic  fibers  pass  to  the  parotid 
gland  and  supply  it  with  vaso-dilator  and  secretory  fibers. 

Practically  all  of  the  vagus  nerve  may  be  regarded  as  belonging 
to  the  visceral  system.  The  jugular  ganglion  represents  its  ganglion 
cell  station.  The  ganglion  of  the  trunk  of  the  vagus  probably  cor- 
responds to  a  posterior  spinal  ganglion  and  is  connected  with  affer- 
ent nerves  of  the  vagus  nerve  only.  As  has  already  been  mentioned, 
it  supplies  motor  fibers  to  the  alimentary  tract  as  far  as  the  ileocolic 
sphincter,  inhibitory  fibers  to  the  heart,  motor  fibers  to  the  bronchi 
and  secretory  fibers  to  the  stomach  and  pancreas. 

Sympathetic  Fibers  of  the  Spinal  Nerves  —  Each  spinal  nerve 
gives  off  fibers  which  participate  in  the  formation  of  the  visceral 
system.  They  are  represented  in  the  anterior  nerve  roots  by  the 
small  medullated  fibers.     (Fig.  153.)     These  leave  the  anterior  divi- 

406 


THE  NERVOUS  SYSTEM 


D 


'o^< 


^l:l5^ 


05i 


ooO' 


Fig.  153. — Sections  across  parts  of  the  roots  of  various  nerves  of  the  dog,  to 
show  the  variations  in  size  of  their  constituent  fibres.     (Quain.) 
(The  nerves  were  stained  with  osmic  acid,  and  the  sections  are  all  drawn 
to  one  scale.) 

A,  from  one  of  the  upper  roots  of  the  accessory. 

B,  a  rootlet  of  the  hypoglossal. 

C,  from  the  first  cervical  ventral  root. 

D,  from  the  second  thoracic  ventral  root. 


sion  of  the  spinal  nerves  and  run  to  one  set  of  ganglia  but  ter- 
minate in  one  of  two  sets  of  ganglia.  One  of  these  sets  of  ganglia 
forms  a  chain  of  ganglia  lying  close  to  the  vertebral  column.  In 
general  there  may  be  said  to  be  one  ganglion  for  each  vertebral 
segment  of  the  column  in  the  thoracic  and  lumbar  region  and  three 
ganglia  for  the  cervical  region. 

The  second  series  of  ganglia  are  the  cardiac  plexus  at  the  root 

408 


THE  NERVOUS  SYSTEM 

of  the  lung  and  base  of  the  heart,  the  solar  plexus  around  the  celiac 
axis,  the  superior  and  inferior  mesenteric  plexuses  around  the  origin 
of  the  superior  and  inferior  mesenteric  arteries,  the  hypogastric 
and  pelvic  plexuses,  in  front  of  the  body  of  the  5th  lumbar  vertebra. 
We  may  call  the  spinal  ganglia  the  lateral  series  of  ganglia  and 
the  ganglia  in  the  large  plexuses  around  the  great  vessels  the  col- 
lateral ganglia.  Another  set  of  plexuses  more  distal  still,  exists  in 
the  walls  of  the  intestines.  They  are  the  plexuses  of  Meissner  and 
Auerbach.     Though  called  terminal  ganglia  they  contain  no  gan- 


SpinaL  ganglion 


Spinal 
cord 


Afferent  fibre 
\  Efferent  fibres 


Sympathetic  afferent  fibres 


Fig.  154. — Plan  of  construction  of  a  typical  spinal  nerve.     (Quain.) 


glion  cells  and  are  rather  to  be  viewed  as  sites  of  interlacing  of 
nerve  fibers  which  suffer  no  interruption  in  passing  through  them. 
All  of  the  sympathetic  nerves  leaving  the  anterior  division  of  the 
spinal  nerves  pass  to  the  spinal  or  lateral  ganglia.  As  they  are 
medullated  they  are  called  white  rami  communicantes.  Some  of 
them  end  in  a  terminal  arborization  around  the  cells  of  these  gan- 
glia ;  others  pass  through  these  ganglia  without  interruption  to  end 
around  cells  in  the  collateral  series  of  ganglia.  All  these  nerve 
fibers  are  called  preganglionic  nerve  fibers.  From  the  cells  around 
which  these  preganglionic  fibers  end  axons  are  given  off  which  are 
non-medullated  and  are  called  post-ganglionic  fibers.  (Figs.  154 
and  155.) 

No  sympathetic  nerve  has  more  than  one  of  these  '  iterruptions 

410 


J 


THE  NERVOUS  SYSTEM 


between  its  origin  and  destination.  Many  of  the  axons  of  the  cells 
in  the  spinal  ganglion  run  back  from  the  ganglion  to  an  anterior 
spinal  nerve,  of  a  different  level,  bend  around  again  to  be  distrib- 
uted with  the  fibers  of  such  an  anterior  or  posterior  spinal  nerve. 

As  they  pass,  therefore,  between  the  ganglia  and  the  spinal 
nerves  they  are  also  called  rami  communicantes,  and  because  they 
are  not  medullated  they  are  called  gray  rami  communicantes. 


Post-ganglionic 
fibre 


Preganglionic  fibre 
in  sympathetic  cord 


PosC-gangllonic  fibre 
in  spinal  nerve 


Pre-gangliohic  fibre 
in  sympathetic  nerve. 

Distal  ganglion 
in  sympath^Cic._ 


Post-gangllonic  fibre 

in,- sympaChttic  nerve   ^^ 


Post-ganglionic  fibre^ 
in  spinal  nerve 


Fig.  155. 


Fibre  in  sympabhetic  cord 
passing  through  two  ganglia 

-Diagram  of  sympathetic.     (Quain.) 


Each  gray  ramus  communicans  is  distributed  to  only  an  area 
of  the  body  which  corresponds  to  the  level  at  which  it  is  given  off. 

A  white  ramus,  on  the  other  hand,  may  run  a  long  distance 
before  it  terminates  around  a  ganglionic  cell  from  which  its  post- 
ganglionic fiber  is  given  off.  Stimulation  of  one  white  ramus  will 
cause  impulses  in  several  gray  rami.  '^ 

412 


THE  NERVOUS  SYSTEM 

The  spinal  ganglia  of  the  upper  three  cervical  nerves  pass  to 
the  superior  cervical  sympathetic  ganglion.  Its  branches  of  distri- 
bution are  to  plexuses  around  the  carotid  arteries  and  their 
branches. 

It  sends  branches  to  the  tympanum  and  to  the  Vidian  nerve  and 
to  the  Gasserian  ganglion.  Many  fibers  reach  the  superior  cervical 
ganglion  from  the  first  five  dorsal  nerves.  These  fibers  reach  it 
after  first  passing  through  the  dorsal  spinal  ganglia.  They  repre- 
sent some  of  the  white  rami  which  have  long  preganglionic  fibers, 
for  their  ganglionic  cells  are  in  the  superior  cervical  ganglion. 
They  convey  the  following  impulses: 

1.  Vaso-constrictor  impulses  to  blood  vessels, 

2.  Dilator  impulses  to  the  pupil, 

3.  Secretory  (trophic?)  impulses  to  the  salivary  and  sweat 
glands, 

4.  Vaso-dilator  fibers  to  the  lower  lip  and  pharynx. 

The  same  five  dorsal  nerves  send  fibers  to  the  stellate  ganglion, 
a  large  ganglion  beneath  the  origin  of  the  subclavian  artery.  It 
communicates  by  two  cords  which  surround  the  subclavian  artery 
with  the  inferior  cervical  ganglion  of  the  sympathetic.  The  ring 
around  the  subclavian  is  called  the  ansa  Vienssens.  The  inferior 
cervical  ganglion  of  the  sympathetic  is  placed  between  the  superior 
and  middle  cervical  ganglion  above,  with  which  it  is  also  connected 
by  two  cords,  and  the  stellate  ganglion  below. 

From  the  cell  stations  of  these  fibers  in  the  stellate  ganglion 
post-ganglionic  fibers  of  the  upper  dorsal  nerves  are  given  off  to 
the  heart. 

They  convey  accelerator  and  augmentor  impulses  to  the  heart. 

Each  spinal  ganglion  is  not  only  connected  with  the  anterior 
spinal  nerve  by  a  gray  and  a  white  ramus  but  also  with  the  ganglia 
above  and  below  it  by  two  connecting  cords. 

The  upper  limbs  are  supplied  by  nerves  coming  from  the  4th  to 
the  11th  dorsal  ganglia. 

They  convey : 

1.  Vaso-constrictor  impulses  to  the  blood  vessels  of  the  limbs, 

2.  Secretory  fibers  to  the  sweat  glands. 

The  lower  limbs  are  supplied  by  branches  of  the  11th  dorsal  to 
the  third  lumbar  ganglion. 
They  convey : 

414 


THE  NERVOUS  SYSTEM 

1.  Vaso-constrictor  impulses  to  the  vessels  of  the  lower  limb, 

2.  Secretory  impulses  to  the  sweat  glands  of  the  lower  limb. 
From  the  lower  6  dorsal  and  upper  3  to  4  lumbar  ganglia  fibers 

pass  to  the  abdominal  viscera. 
They  convey : 

1.  Vaso-constrictor  fibers  to  the  vessels  of  the  stomach  and 
small  intestines,  the  kidney  and  spleen, 

2.  Probably  vaso-dilator  fibers  as  well, 

3.  Muscular  inhibitory  impulses  to  the  stomach  and  small  in- 
testines, 

4.  Motor  fibers  for  the  ileocolic  sphincter. 

Nerves  from  the  lower  dorsal  and  upper  3  to  4  lumbar  nerves 
pass  to  the  pelvic  plexus  in  two  strong  cords  running  as  the  hypo- 
gastric nerves  from  the  inferior  mesenteric  plexus  to  the  pelvic 
plexus. 

They  convey : 

1.  Vaso-constrictor  impulses  to  the  vessels  of  the  viscera, 

2.  Inhibitory  impulses  to  the  colon, 

3.  Both  motor  and  inhibitory  impulses  to  the  bladder, 

4.  Motor  fibers  to  the  retractor  penis, 

5.  Motor  fibers  to  the  uterus  and  vagina. 

Besides  the  autonomic  fibers  passing  in  the  hypogastric  nerves 
from  the  inferior  mesenteric  plexus  to  the  pelvic  plexus,  the  an- 
terior branches  of  the  second  to  the  fourth  sacral  nerves  furnish 
branches  of  autonomic  fibers  which,  without  making  connections 
with  any  lateral  ganglia,  unite  to  form  on  each  side  the  nervus 
Erigens.  This  nerve  passes  directly  to  the  pelvic  plexus  in  which 
its  fibers  suffer  interruption. 

They  convey : 

1.  Motor  impulses  to  the  bladder,  descending  colon  and  rectum, 

2.  Vaso-motor  impulses  to  the  vessels  of  the  pelvic  viscera, 

3.  Inhibitory  fibers  to  the  sphincter  of  the  bladder, 

4.  Dilator  fibers  to  the  vessels  of  the  penis  and  inhibitory  fibers 
to  the  retractor  penis. 


416 


QUESTIONS  AND  ANSWERS 

Pages  4-8 

Q.  What  is  the  function  which  the  nervous  system  has  been  developed  to 
perform? 

A.  To  make  possible  the  rapid  transmission  between  distant  portions  of 
the  body  of  changes  in  the  environment  of  groups  of  cells. 

Q.  What  important  stages  in  the  development  of  a  central  nervous  system 
are  represented  by  the  nervous  systems  of  jiiyertebrates? " — 

A.  The  peripherally  placed  nervous  system  of  a  hydra  in  which  there  is 
but  slight  difference  between  the  protective  surface  epithelial  cell  and 
the  specialized  sensitive  and  conductive  epithelial  cell,  and  in  which  the  sensi- 
tive cell,  the  conductive  portion  and  contractile  tissue  constitute  one  cell. 
{Page  4.) 

The  peripherally  placed  nervous  system  of  the  jellyfish  in  which  the 
conductive  tissue  forms  a  ring  about  the  periphery  of  the  animal,  separated 
from  the  surface  epithelium  and  contractive  tissue  but  connected  to  both  and 
to  different  portions  of  itself  by  its  own  fiberlike  processes.       {Page  8.) 

The  centrally  placed  nervous  system  of  the  ■ggrip,  and  of  the  still  more 
advanced  crayfish  r  in  both  the  cells  of  the  conductive  tissue  are  centrally 
placed,  thus  facilitating  communication  between  different  portions  of  itself 
and  occupying  the  most  efficient  p)3sition  for  rapid  communication  with  any 
portion  of  the  periphery.  In  the  more  advanced  crayfish  there  is  a  special, 
development  of  the  fore  part  of  the  central  chain  of  nerve  tissue,  thus  facili- 
tating a  quick  appreciation  of  changes  of  the  environment  in  the  direction 
in  which  the  animal  moves.     {Page  12.) 

Page  14  ^/^" 

Q.  How  is  the  nervous  system  of  mammals  developed  from  the  cells  of 
the  embryo? 

A.  By  the  infolding  of  the  .epiblast,  corresponding  to  the  dorsum  of 
that  group  of  cells  of  embryo  from  which  all  this  tissue  of  the  foetus  are 
developed,  there  is  formed  the  neural  canal,  and  on  each  side  a  depressed  cord 
of  cells.  By  a  differentiation  of  the  cells  lining  the  canal  and  forming  the 
cord  the  primitive  spongioblasts  and  neuroblasts  are  formed.  Both  these 
develop  processes.  The  spongioblasts  with  their  processes  form  the  neuroglia 
or  supporting  tissue  of  the  nervous  system.  The  neuroblasts  of  the  neural 
canal  form  nerve  cells  and  their  processes  the  motor  nerves.  These  grow  out 
into  the  body  of  the  embryo  and  form  connections  with  every  active  tissue. 
The  neuroblasts  of  the  lateral  cords  of  cells  develop  into  the  nerve  cells  of  the 
sensory  ganglia.  They  develop  two  processes,  one  forming  peripheral  connec- 
tibiis  witfi^tfie^ various  specialized  sensitive  cells  of  the  body,  and  the  other 
growing  centrally  among  the  cells  developing  from  the  neural  canal  to  partici- 
pate in  the  formation  of  central  synapses. 

^  418 


THE  NERVOUS  SYSTEM 

Page  34 

Q.  Describe  a  neuron. 

A.  A  neuron  consists  of  a  nerve  cell  and  its  processes.     A  nerve  cell  pos- 
sesses the  following  parts:     See  text. 

A  nerve  has  the  following  structure:     See  text. 

Fage  54 
Q.  Describe  the  different  peripheral  endings  of  nerves. 


V/Q 


A.  See  text,  and  divide  into  sensory  and  motor  nerve  endings. 

Page  12 


Q.  Classify  nerves,  v* 
A.  See  text. 

Page  74 

Q.  Describe  the  method  of  measuring  the  velocity  of  nerve  impulses  for 
both  motor  and  sensory  nerves. 
A.  See  text. 

Q.  In  what  direction  does  a  nerve  impulse  travel?  t  J ^ 

A.  In  both  directions  from  the  stimulated  point.  •  i>-«,ot^  i?%v>» 

Page  76 

Q.  Is  there  any  expenditure  of  energy  caused  by  the  passage  of  a  nerve 
impulse,  how  much  and  how  is  it  estimated? 

A.  A  very  small  amount,  not  enough  to  be  indicated  by  its  transformation 
into  heat,  but  only  by  the  consumption  of  oxygen. 

Page  78 

Q.  What  is  the  demarcation  current? 

A.  The  current  excited  in  a  nerve  by  the  degenerating  changes  following 
injury  to  the  nerve. 

^'     Q.  What  is  the  current  of  action? 

A.  The  current  which  always  accompanies  the  passage  of  a  nerve  impulse. 

Q.  In  a  muscle  nerve  preparation  in  what  order  dp  the  tissues  become 
fatigued? 

A.  Motor  end  plate,  muscle.     The  nerve  is  not  known  to  become  fatigued. 


I 

J 


/ 


Page  84 

Q.  What  is  summation? 
A.  The   reaction   evoked   by   the   combined   effect   of   several   sub-minimal 
stimuli  following  each  other  at  the  proper  favorable  interval. 

Q.  What  is  the  refractory  period? 

A.  The   period   following  an   excitation   during   which   the   nerve   remains 
incapable  of  response  to  a  second  stimulus. 

"  420 


v-^\J  i  ^-CXs^  '^K^yWtA.^v/C  ^tvto^JK 


Vi/s^^_,^£>iaJ^    CXUy<A^^x 


■ty 


THE  NERVOUS  SYSTEM 

Fage  86 

Q.  At  what  electrode  does  excitation  of  a  nerve  by  an  electrical  current 
take  place? 

A.  At  the  cathode  at  the  make,  and  anode  at  the  break. 

Q.  What  changes  in  degrees  of  excitability  do  these  special  sites  of  exci- 
tation indicate  and  what  names  are  made  use  of  to  express  such  changes? 

A.  They  indicate  changes  in  excitability  which  are  proportional  to  the 
response  evoked,  that  change  occurring  at  the  cathode  being  named  cathelec- 
trotones,  and  at  the  anode,  anelectrotones,  so  that  the  development  of  the  one 
and  passing  off  of  the  other  is  what  causes  excitation. 

Fage  90 

Q.  How  much  of  the  nerve  may  be  involved  in  anelectrotones  or  cath- 
electrotones? 

A.  The  greater  the  strength  of  the  current  the  greater  the  length  of  the 
n&we  which  is  in  anelectrotonus,  the  remainder  of  the  nerve  being  in  catelec- 
trotonus. 

Q.  What  effect  do  the  facts  expressed  in  the  last  answer  have  upon  the 
passage  of  the  nerve  impulse  and  what  name  is  given  to  the  phenomenon? 

A.  The  nerve  impulse  may  be  blocked  at  the  anode  by  a  high  degree  of 
anelectrotones  or  at  the  cathode  by  a  swing  back  from  a  very  high  state  of 
cathelectrotones  to  a  very  low  state  of  cathelectrotones.  The  phenomena 
result  in  a  response  to  stimulation  which  is  different  for  different  strengths 
of  the  current  used,  and  this  fact  is  called  Pfliiger  's  law. 

Fage  94 

Q.  What  is  the  order  of  strength  of  contraction  in  the  human  being  when 
the  electrode  must  be  applied  on  the  surface  of  the  skin  at  a  distance  from 
the  nerve,  and  why  is  this  order  different  from  that  order  to  be  expected  when 
the  electrodes  are  applied  directly  to  the  nerves  according  to  Pfliiger 's  law? 
A.  1,  See  text  for  order. 

2.  Because  there  is  a  greater  strength  of  current,  due  to  convergence 
of  the  lines  of  force  between  the  electrodes,  in  that  portion  of 
the  nerve  which  is  nearest  to  the  stimulating  electrode. 

Fage  96 

Q.  What  is  the  current  of  polarization  and  to  what  is  it  due? 

A.  The  current  of  polarization  is  a  current  independent  of  vital  changes 
occurring  in  an  electrically  stimulated  nerve,  and  is  due  to  the  difference  in 
potential  which  depends  upon  the  collection  of  ions  upon  the  electrodes  and 
bearing  an  opposite  charge  to  the  electrodes.  These  ions  arise  in  the  elec- 
trolyte of  the  nerve  sheath,  and  the  phenomenon  is  common  to  any  electrolyte 
carrying  a  current. 

Page  100 

Q.  What  are  the  conditions  affecting  the  excitatory  effect  in  an  electri- 
cally  stimulated  nerve? 

A.  1.  The  rate  of  change  in  the  make  or  break.     There  is  an  optional 
rate  of  change. 
2.  The  intensity  of  the  current.     There  is  an  optional  intensity. 

422 


J 


THE  NERVOUS  SYSTEM 

3.  The  duration  of  the  current.     There  is  an  optional  duration.     This 

duration  is  different  for  nerve,  motor  end  plate  and  muscle. 

4.  The  temperature.     Warming  the  nerve  of  mammal  increases  its  irri- 

tability. 

Fage  104 

Q.  In  what  direction  may  an  impulse  pass  across  a  motor  end  plate? 
A.  As  is  the  case  in  all  synapses,  only  in  the  normal  direction, 

Fage  110 

Q.  Describe  the  gross  anatomy  of  the  spinal  cord. 
A.  See  text. 

Fage  116 

Q.  What  are  the  groups  of  nerve  cells  in  the  gray  matter? 
,  A.  1.  Anterior  horn  ^lls.     The  motor  cells. 

2.  Small  cells  in  the  lateral  portion  of  the  base  of  the  anterior  horn, 

the  motor  cgils  of  the  sympathetic  nerves. 

3.  Cells   in   ;^e    lateral  portion   of    the    base    of    the   posterior   horn, 

Clarke's  column, i&be  axons  of  which  form  the  dorso-late;Fal  cere- 
bellar tract.  V"  -  "^ 

4.  Cells  of  the  posterior \horn,   many  of  which  are   receiving  cells  of 

"'     fibers  of  the  posterior  nerve  roots,  and  others  association  cells. 

Fage  120 

Q.  What  are  some  of  the  methods  of  tracing  the  systems  of  neurons? 
A.  The  Myelination  Method.     See  text  for  explanation. 
The  Wallerian  Method.    See  text  for  explanation. 

Fage  126 

I 
^Q.  What  is  the  termination  of  the  fibers  of  the  posterior  nerve  roots? 
A.  There  are  5  sets  of  fibfixs-:  those  forming 

1.  Lissauer  's  column. 

2.  The  columns  of  GoU  and  Burdach. 

3.  The  fibers  ending  in   the   cells  of   the   posterior   horn,    from  which 

impulses  are  carried  onward  .to  the  ant^rio*  lateral  column  of 
the  opposite  side,'to  the  anterior  horn  of  same  sid^  to  posterior 
horn  of  opposite  side, \  to  Clarke's  columns  of  cells^'to  small 
cells  oTTaleraT  horn.      ^^^i^.  o^  a-cr.    „  h^  i  V/ 

Fage  136 

1-'    Q.  What  are  the  descending  spinal  tracts? 
A.  See  text. 

Page  140 

Q.   What  are  the  ascending  spinal  tracts? 
V        A.  See  text. 
^  )  Fage  142 

♦mJ.  What  sensory  impulses  are  carried  by  the  various  ascending  tracts? 
A.  See  text. 

424 ,;/-, 


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h^^ioe^l '^ox^-  loiJ  T^ilf^  '^    ^^^xA^tl^  ?^  ^% 


--^y-^j-v... ..  -  --f:^  -^  -{£,.  ^^'s^ 


THE  NERVOUS  SYSTEM 


Page  144 


Q.  What  are  the  symptoms  of  unilateral  section  of  the  spinal  cord? 
A.  See  text. 

Q.  How  may  the  spinal  functions  be  studied  to  the  best  advantage  and 


A.  By  dividing  the  cord  from  the  brain,  because  the  functions  of  the 
cord  will  thus  be  undisturbed  by  impulses  from  the  brain. 

Tage  146 

Q.  What  condition  is  induced  by  separation  of  the  cord  from  the  brain, 
and  what  are  the  symptoms? 
A.  1.  Spinal  shock.  • 

2.  Permanent  loss   of  sensation   and  of  voluntary  motion  below  level 

of  lesion. 

3.  Temporary   loss   of   muscular   tone,   of  vascular  tone  and   of  reflex 

~"  response.  "^ 

Q.  To  what  are  the  symptoms  of  spinal  shock  due? 

A.  The  permanent  symptoms  are  due  to  division  of  the  paths  of  sensory 
perception  and  voluntary  motor  impulses.  The  temporary  symptoms  are  due 
to  the  division  of  paths  through  which,  under  normal  conditions,  impulses 
responsible  for  both  vascular  and  skeletal  tone  are  constantly  passing.  These 
paths  include  in  part  ascending  tracts. 


' by  spi^aly 


/  Page  150  ((MAS^^-^-  ^^Hi-UtM^ 

Q.  Define   reflex  action,  explain  its  mechanism,  and  .illustrate 
reflexes.  A  - 

A.  A  reflex  action  is  any  motor  response  produced  by  a"sensory  stimulus. 
It  involves  an  afferent  limb,  or  sensory  neuron,  conveying  the  sensory  stimulus 
to  the  central  nervous  system,  one  or  more  central  synapses,  across  which  the 
sensory  stimulus  is  transmitted  to  the.  motor  or  efferent  neuron.  It  is  illus- 
trated by  the  scratch  reflex,  sole  reflex,  vascular  reflex,  bladder  and  rectal 
reflexes.  The  reflexes  upon  which  muscular  tone  depends  and  tendon  reflexes. 
See  text  for  description. 

Page  156 
t/ 
Q.  What  are  the  characteristics  of  spinal  reflexes? 
A.  Purpose  like,  etc.     See  text.  "5** 

Page  172 

Q.  Define  and  describe   a  synapse  and  what  is  its  function? 

A.  A  synapse  is  the  interval  between  the  terminal  arborizations  of  a 
nerve  fiber  around  the  cell  of  another  neuron  with  which  it  is  functionally 
related.  This  interval  is  not  bridged  by  nerve  fibrillae,  so  that  there  is  no 
direct  continuation  of  nerve  substance  between  one  neuron  and  the  next  one 
in  functional  association  with  it.,  The  interval  is  filled  with  a  granular 
material  which  permits  of  the  pas^ge  of  nerve  impulses  in  only  one  direction. 

V    426 


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THE  NERVOUS  SYSTEM 

Page  176 

Q,  What  is  meant  by  the  trophic  functions  of  the  spinal  cord? 
A.  The    spinal    cord    is    constantly    supplying    to    the    peripheral    tissues 
through   special  nerve   impulses,   named   trophic,   which  improve  the  nutrition 
of  these  tissues. 
■^  Page  178 

Q.  How  must  the  brain  be  considered  phylogenetically  and  from  what 
embryological  units  does  it  develop? 

A,  As  modified  anterior  segments  of  the  primitive  cerebro-spinal  axis 
or  canal.  The  four  divisions,  into  which  the  adult  brain  may  be  grossly 
divided,  develop  from  three  primitive  cerebral  cavities  at  the  anterior  end  of 
the  primitive  neural  tube.  These  three  vesicles  are  named  anterior,  middle 
and  posterior  cerebral  vesicles.  The  anterior  vesicle  develops  into  the  lateral 
ventricles  and  cerebral  cortex  and  third  ventricles  of  the  thalami^^  The  middle 
vesicle  into -the  aqueduct  of  Sylvius  and  the  brain  stem  with  its  nuclei.  -The 
posterior  vesicle  into  the  fourth  ventricle,  the  pons,  cerebellum  and  bulb.X^ 


,^Z 


Page  180 


Q.  How  are  the  retina  of  the  eyes,  the  optic  nerves,  the  olfactory  bulbs 
and  olfactory  nerves  developed? 

A.  By  tubular  protrusions  from   the   anterior  cerebral  vesicles. 

v'  Page  182 

l^~~    Q.  Describe  the  floor  of  the   fourth  ventricle? 
A.  See  text. 

Page  186  ■ 

Q.  Describe  the  third  brain.—  t'--     C     "i^^ 

A.  See   text.     Mention   iter    of   Sylvius   and    corpora    quadrigemina   and 
^  geniculate  bodies  and  their  connections. 

Q.  Describe  the  third  ventricle. 

A.  See  text.  Mention  its  shape,  its  roof,  the  corpus  callosum  and  fornix, 
its  lateral  walls,  the  optic  thalami,  its  three  commissures,  and  in  the  floor 
the  optic  chiasma,  the  pituitary  body  and  at  its  posterior  corner  the  pineal 
gland.  ^    , 

'  Page  192  \  -/j 

^    Q.  Describe  the  lateral  ventricles. 

A.  See  text.  Mention  the  body  and  three  horns.  The  roof  is  formed  by 
the  corpus  callosum ;  the  floor  of  ihe^^dy  and  roof  of  the  inferior  horn;  by  the 
optic  thalarni,  the  stria  semicireularis  and  caudate  nucleus  with  its  tail,  the 
-^  internal  wallSy  the  septum  lucidum  (anterior  horn),  the  fornix  and  the  choroid 
plexus  (body)  ;  and  from  above  down,  the  forceps  major  and  hippocampus 
minor  or  calcar  avis  (the  posterior  horn),  the  choroid  plexus  and  hippo- 
campus major  (inferior  horn)*  The  external  wall  of  jLll..horns  and  body  by 
the  cerebral  convolutions.  The  lateral  ventricles  communicate  with  the  third 
ventricles  by  the  foramen  of  Monro,  which  opens  into  the  anterior  end  of 
the  third  ventricle  beneath  andjsehind  the  pillar  of  the  fornix,  from  the 
juncture  of  the  anterior  horn  and  body  of  the  lateral  ventricle.     It  is  the 

428 


A^ 


f;i-e^  ~hoyM...^J^^(lJ^-^  V-     '^f 


THE  NERVOUS  SYSTEM 

remnant  of  the  neck  of  the  bud  from  the  primitive  anterior  cerebral  vesicle, 
the  cavity  of  whicE"forms  the  lateral  ventricles  and  the  eye  walls. 

Page  204  y^ 

,-'Q,  Describe  the  cerebral  hemispheres. 
A.  The  cerebral  hemispheres  are  divided  into  five  krSes  by  four  important 
fissures.  The  fissure  of  Eolando  (see  text  for  position)  separates  the  frontal 
lobe  on  the  external  surface  of  brain  from  the  parietal  lobe.  The  fissure 
of  Sylvius  (see  text  for  position)  forms  the  lower  boundary  of  the  frontal 
lobe  and  parietal  lobe  on  the  external  surface,  separating  them  from  the 
temporal  lobes^.  The,  parietooccipital  fissure  (see  text  for  position),  which 
separates  the  occipital  lobe  from  the  parietal  and  limbic  lobes  on  the  internal' 
surface  of  the  hemispheres,  and  in4ieates  the  separation  of  the  occipital'from 
the  parietal  and  temporal  lobes  on  the  external  surface  of  the  hemispheres.         -_ 

V^  ^0.9^  S3 4 

Q.  Describe  the  internal  structure  of  the  medulla. 

A.  The  internal  structure  of  the  medulla  differs  from  that  of  the  spinal 
cord  as  a  result  of  the  opening  out  of  the  central  canal  of  the  cord  into  the 
fourth  ventricle  of  the  bulb.  The  disposition  of  the  gray  matter  represents 
a  displacement  of  the  gray  matter  of  the  cord  in  a  posterior  and  then  a 
lateral  direction  to  a  position  lateral  in  the  floor  of  the  ventricle^  In  this 
position  it  forms  the  nuclei  of  the  cranial  nerves  in  the  positions',  described 
and  illustrated  in  the  text.  '^^._  ,;)    '4  ^-V"H 

A  second  difference  between  the  internal  structure  of  the  medulla  and 
the  cord  is  dueCt(|  the  passage  of  the  fibers  of  the  pyramidal  tract  from  the 
decussation  on  the  front  to  the  posterolateral  position  which  they  occupy  in 
the  cord.-  J[n  this  passage  they  amputate  and  break  up  tlie  gray  matter-of 
the  anterior  horns,  forming  the  lateral  nucleus.  _^  L' 

A  third  difference  is  due  to  the  development  of  nejv  gray  matter,  the 
ni^cleus  gracilis  and  cuneatus^  ia-the  posterolateral  regions  of  the  bulb  in 
which  the  columns  of  Goll  and  Burdach  end.  Another  important  mass  of 
gray  matter  appearing  in  the  upper  part  of  the  bulb  is  the^olivary  nucleus.-^ 
On  section  it  appears  scalloped  shaped,  with  its  concavity  directed  toward  the 
center  of  the  bulb.  Its  efferent  fibers  are  afferent  to  the  cortex  of  the  cere-  . 
beHum.  jfl  Vl'-^J  \  .1-i.M-lVu^. 

Q.  Describe  the  cerebeltmrJ^l^tA.  «)%    ^"^   %~^k' 

A.  The  cerebellum  is  an  isolatetl^ass  of  brain  tissue  about  2l^"  x  1^4"> 
situated  in  the  posterior  fossa  of  the  cranium  and  composed  of  two  lateral 
lobes  and  a  central  mass,  forming 'a  rounded  intervening  eminence  above  and 
below.  The  surface  of  all  these  three  lobes  is  thrown  into  convolutions  and 
contains  immediately  beneath  it  the  gray  matter  of  the  cerebellum.  The 
tissue  beneath  this  surface  layer  co^isists  of  white  fibers  which  enter  -for 
the  most  part  the  cerebellum  in'tlie  three  peduncles  and  pass  to  the  cells  in 
the  gray  matter^  Within  the  center  of  the  cerebellum  are  four  nuclei  (see 
text), "which  receive  the  efferent  fibers  from  the  gray  matter  of  the  cortex  and 

'"\)  430 


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,  THE  NERVOUS  SYSTEM  ,    .        - 

V  /  -"  ^ 

.,B^d  efferent  fibers  from  the  cerebelluip  to  the  nuclei  pontis  arid  red  nucleus. 

y  WMie  many  fibers  passing,  to.  the  eerejbjellum  probably  make  connections  with 

the  deep  nuclei,  particularly  those i^rbm  the  vestibular   and  Deiters'  nucleO 

;.'■©*  in_  general  the  afferent   fibers  to   the   cerebellum  pass  to   the  corte^^  ang 

the  efferent  fibers  pass  out  from  its  deep  nuclei.     The- afferent  fibers  to  the 

>-t— Cerebellum -pass  to  it^  through  the  three  peduncles  (see  text,  page  298). 

^      y  Page  26€  ^ 

\     V     Q.  Describe  the  third  brain. 

A.  Above  the  pons  the  central  canal  of  the  cerebro-spinal  systeulTbecomes" 
again   a   closed   narrow   canal,   until   it   opens   into   the   third   ventricle.      The 
gray  matter  immediately  surrounding  j^  constitutes  the  nuclei  of  the  oculo- 
motor nerves..     The  superior  peduncles  of  the   cerebellum  converge  below  the 
canal  to  cross  in  a  decussation  and  end  in  the  cells  of  red  nucleus,-  a  large 
mass  of  gray  matter  situated  in-  the  substance  -.of- the  third  brain  bglow  the    .  ^ 
forepart  of  the  aqueduetus  Sylvii.    Above  the  forepart  of  the  aqueduct,  fown-  --fc* 
ing   rounded   eminences   on   the    dorsal   surface    of   the   third   brain,    are   two  I 
masses  of  gray  matter  on  each  side  of  the  middle  line,  the  superior  and  inferior 
corpora  quadrigemina.     The  superior  corpora  quadrigeminaf receive  fibers  from 
the  optic  nerve  and  cerebellum.     The  inferior  corpora  quadrigemina*' receives     A 
the  lateral  fillet  and  is  related  in  function  to  the  sense  of  hearing.      '       \     ^rvj 

^  Page  S62  ^^'f 

Q. .What  is  the  posterior  longitudinal  bundle  and  its  function? 
'"■-  A.  A  longitudinal  bundle  of  nerve  fibers  is-seea-in-all  sections  of -the  third 

brain  just  ventral  to  the  Sylvian  aqueduct  and  is  continued  downwards  through 
the  pons  and  medulla,  being  continuous  with  the  tract  of  Marie  or  the 
anterolateral  association  tracts  of  the  spinal  cord.  By  means  of  this'  tract 
a  connection  is  established  between  all  the  nuclei  of  the  cranial  nerve.  See 
Fig.  126. 

Page  304 

-''    Q.  Describe  the  subcortical  masses  of  gray  matter,  and  the  external  and  .' 
internal  capsule;  \V,  ■ 

A.  The  subcortical  nuclei,  apart  from  those  belonging  to  the  third  brain, 
gjje  the  cjlaustrum,  the  lenticular  nucleus,  the  caudate  nucleus  and  the  optic 
thalami.  " 

The  craiustrum  is  a  thin  mass  of  gray  matter  immediately  underlying 
the  Island  of  Eeil,  being  separated  from  it  by  a  thin  layer  of  white  matter. 

//''^yf^    The  lenticular  nucleus,  consisting  of  the  putamen  and  the  globus  pallidus, 

/^is  a   wedged   shaped    (on  coronal   section)    mass  of,  gray  matter  immediately 

\^nternal  to  the  claustrum   and   separated  from  it  by  a  thin  layer  of  whi|p 

matter,  the  external  capsule.  "" 

The  caudate  nucleus  is  a  large  mass  of  gray  matter  consisting  of  a 
rounded  anterior  head  and  a  long  tail  tapering  out  posteriorly,  the  whole 
body  being  shaped  somewhat  like  a  long  turnip  or  drawn-out  pear.,  -  •!% 
curves  around  the  external  peri^ery  of  the  optic  thalamus,  forming  the  ex- 
ternal part  of  the  flojr  of  the  body  of  the  lateral  ventricle  and  the  roof  of 
•  the  external  part  of  the  inferior  horn.    It  aiui-*ke  optic  thalamus, -whicini^iii 

432      b 


THE  NERVOUS  SYSTEM 

i\     part,  riTinirrlrnj  is  separated  from  the  lenticular  nucleus  by  an  important  mass 
of ■'pHK  mflj^^-,  the  internal  capsule. 

^Tne  optic  thalamus  itself  is  a  large   mass  of   gray  matter   forming  the 
external  wall  of  the  third  ventricle  and  the  floor  of  the  lateral  ventricle  and       * 
bounded  externally  by  the  internal  capsule  and  in  part  by  the  caudate  nucleus. 

Page  SOS 

Q.  Describe  the  internal  capsule,  the  pyramidal  tracts  and  the  cerebrp- 
pontine  tracts.  i 

A.  The  internal  capsule  is  a  thick  stratum  of  white  fibers  passing  in  a 
general  vertical   direction  between  the  cerebral  cortex  and  the  pons.     It  is 
flanked  by  the  optic  thj^lamus  internally  and  the  lenticular  nucleus  externally. 
Its  fibers  pass  To~and  from  all  "parts  of  the  cerebral  cortex/   Below,  ihey^on- 
stitute  the^^ura  cerebLrij._;fpTming  a   great  thick  bundle  on  each  side  of  the  ^^ 
middle   line   ventral   to   the   third   brain,    and-  converging^  to   plunge__iii±o    the  ^ 
upper  part  of  the  pons.     See  Figs.  100,  135. J'  Through  it^-mijCBIl  the  sensory  .-rv* 
tracts   from    the ,  optic    thalamij^eontinuing   onw^,r4   the   mesial- -  fillet   to    the    <^ 
^eerebral  cortex; -also   within  it  pass  the  large  motor  tracts  made  of  fibers    - 
^, which  ^re   the   axis  cylinders  of   the  cells   of   the  motor  area  of   the   cortev^''^ 
These   pass   down   through   the    central   regions    of   the    internal   capsule    and 
crura  cerebri'^  the  pons.     They  plunge  through  the  anterior  portion  of  the 
substance  of  the  pons  and   appear  on  eaeir^sitle   of  the   middle  line   of  the 
anterior  surface  of  the  medulla,  where  they  constitute  the  two  rounded  emi- 
nences known  as  the  pyraniids  Ji,  Iinmediately  below  the  pyramids -they  decus- 
sate and  pass  downward  in  the-^ateral  columns  of  the  cord  as  the  pyramidal 
tracts,  to  terminate  at  various  levels  of  the  cord,  either  directly  or  indirectly 
around   the   anterior  horn   cells./   The  internal   capsule   also   contains   fronto- 
pontine   and  temporopontine   fibers,   passing  from  the   frontal   and   temporal 
lobes   through  ~fEe~anterior   and   posterior   limbs   respectively   of   the   internal 
capsule  and  the  medial  and  external  portions  respectively  of  the  crura  to  the 
cells  of  the  forma'tio  reticularis. 

Tage  S36 

Q.  What  are  the  portions  of  the  olfactory  mechanism  in  their  physiological 
order? 

A.  1.  The  peripheral  bipolar  cells  in  the  nasal  mucosa. 

2.  The  arborizing  connection  between  the  central  process  of  these  cells 

and  the  peripheral  processes  of  the  mitral  cells. 

3.  The  mitral  cells  in  the  olfactory  bulbs. 

4.  The  olfactory  tracts. 

5.  The  portions  of  the  brain  and  their  connecting  tracts  which  form 

the  olfactory  mechanism.     See  text. 

Page  340 

Q.  Describe  the  optic  nerves? 

A.  The  optic  nerves  are  two  large  bundle  of  nerve  fibers,  these  fibers 
being  axons  of  the  ganglion  cells  in  the  anterior  laj^ers  of  the  retinae,  which  pass 
through  the  optic  foramen  to  the  optic  grooVe  on  the  upper  surface  of  the 
body  of  the  sphenoid.     In  this  groove  the  fibers  from  the  inner  half  of  each 

434 


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^"^ttHwH 


THE  NERVOUS  SYSTEM 

retina  decussate  and  pass  them  with  the  fibers  from  the  external  half  of 
each  retina  in  two  large  bundles,  the  optic  tracts,  around  the  crura  cerebri 
(see  Fig.  100)  to  the  external  geniculate  body,  the  superior  corpora  quad- 
rigemina  and  the  posterior  portion  of  the  optic  thalamic  Axons  of  cells  in 
these  nuclei  then  continue  the  visual  sensations  through  the  posterior  portion-— 
of  the  internal  capsule,  the  optic  radiations,  to  the  occipital  lobes.         ^ 

Page  344,  0^  .J^"        J^'^"^^  r^ 

Q.  What  are  the  oeulo-motor  nerves  a^d  their  function?  ,0' 
A.  The  oculo-motor  nerves  are  the  third,  fourth  and  sixth.  The  nuclei 
of  origen  of  the  third  and  fourth  surround  the  Sylvian  aqueduct.  That  of 
the  sixth  is  beneath  the  floor  of  the  pontine  portion  of  the  medulla.  They 
supply  oculo-motor  impulses  to  the  recti  muscles  of  the  eyeball^-the  sixth 
supplying  the  external  rectus,  the  fourth  the  superior  oblique  and  the  third 
:^  the  other  muscles  and  sphincter  pupili  and  ciliary  muscleN,^^'  ^ 

Q.  What  is  the  function  of  the  fifth  nerve?    —        '       "^     </  "^^^^j^-^tyit 

A.  See  text.  ^'"  ^  ^  ^^^-^^ 

Q.  What  is  the  function  of  the  seventh  nerve  ?  Ji  -^£ 

A.  See  text.  — -^_^  /^^UfT' 

Page  346  ^"' 

^     Q.  What  is  the  function  of  the  eighth  nerve,  and  the  central  connections 
of  its  fibers? 

A.  The   eight  nerve  supplies  to  the  central  nervous  system  two   sets  of 
impulses  through  the  two  separate  portions  of  which  it  consists. 

1.  The  vestibular  portion  is  composed  of  axons  of  bipolar  nerve  cells 

which  have  retained  their  original  bipolar  morphology,  and  the 
peripheral  processes  of  which  end  in  the  saccule,  vestibule  and 
semicircular  canals.  It  therefore  transmits  sensations  of  equilib- 
rium. The  central  processes  end  in  the  vestibular  nucleus  be- 
neath the  mid-lateral  portion  of  the  floor  of  the  fourth  ven- 
tricle. Its  axons  form  important  connections  with  Dieters' 
and  Bechterew's  nuclei,  two  very  important  nuclei  in  the  same 
region.  From  these  nuclei  fibers  pass  to  the  roof  nuclei  and 
cortex  of  the  cerebellum.  Doubtless  some  fibers  of  the  vestibular 
nucleus  pass  directly  to  the  roof  nuclei  of  the  cerebellum.  They 
transmit  impulses  excited  by  changes  in  the  position  of  the  body 
as  a  whole. 

2.  The  auditory  portion  of  the  eighth  nerve  arises  in  the  bipolar  cells 

situated  in  the  crest  of  the  cochlea.  These  also  have  retained 
their  embryonic  bipolar  morphology.  Their  peripheral  processes 
terminate  in  the  auditory  epithelium  of  the  canal  of  Corti. 
Their  central  processes  end  in  the  cells  of  the  auditory  tubercle 
at  the  extreme  mid-lateral  angle  of  the  floor  of  the  medulla. 
The  impulses  are  carried  across  the  middle  line  to  the  opposite 
side  of  the  medulla  to  form  the  ascending  tract  of  the  lateral 
fillet  by  two  sets  of  fibers,  one  superficial  on  the  floor  of  the 
medulla,  the  stria  acoustica,  and  the  other  running  directly  to 
the  lateral  fillet  forming  a  decussation  imbedded  deeply  in  the 
medulla  and  known  as  the  trapezium.  By  means  of  the  lateral 
fillet  the  impulses  pass  to  the  internal  geniculate  body  and  the 

436 


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THE  NERVOUS  SYSTEM 

inferior  corpora  quadrigemina,  and  thence  through  the  internal 
capsule  and  finally  by  the  auditory  radiations  to  the  temporal 
convolutions. 

Tage  350 

Q.  What  is  the  function  of  the  ninth,  tenth  and  twelfth  nerves? 
A.  See  text. 

Q.  How  may  the  functions  of  the  brain  be  studied? 
A.  See  text. 

Fage  352 

Q.  What  are  the  afferent  impulses  received  by  the  medulla? 
A.  See  text. 

Q.  Describe  the  activities  of  the  bulbo-spinal  animal  and  how  it  differs 
from  the  spinal  animal. 

A.  Its  cardiac,"  arterial  and  respiratory  functions  are  normal.  There  is 
a  little  greater  stability  of  the  spinal  reflexes,  due  to  the  preservation  of  a 
little  greater  degree  of  muscular  tone.  '^.^"^ 

Tage  354 

Q.  Describe  the  activities  of  the  pontine-bulbo-spinal  animal. 

A.  It  shows  all  the  reactions  of  the  bulbo-spinal  animal,  but  its  position 
and  movements  wiU  preserve  the  normal  position  of  its  center  of  gravity. 
There  is  greater  increase  in  the  stability  of/ reflex  Ha©¥efiaent.  If  such  an 
animal  loses  its  cerebellum  it  becomes  spontaneously  active. 

Q.  Describe  the  activities  of  the  midbrain-bulbo-spinal  animal. 
A.  The  mammal  exhibits   decerebrate  rigidity    (see  text   for   definition) 
and  of  course  all  the  activities  of  which  the  pontine-bulbo-spinal  animal  is 
capable. 

The  frog  exhibits  little  that  is  abnormal  in  its  deportment. 

Fage  356 

Q.  Describe  the  deportment  of  the  thalamo-spinal  animal. 

A.  Its  deportment  exhibits  so  little  that  is  abnormal  that  only  unusual 
tests  designed  to  bring  into  play  activities  which  involve  the  exercise  of 
memory,  and  therefore  choice,  fear,  affection,  etc.,  are  capable  of  detecting 
anything  abnormal. 

Q.  What  are  the  functions  of  the  cerebellum? 

A.  The  cerebellum  is  the  receiving  station  for  the  important  nerves  of 
both  proprioceptive  and  exteroceptive  impulses  of  static  sensation.  The  end- 
ings of  these  nerves  are  so  associated  with  association  neurons  of  the  cerebrum, 
including  the  efferent  control  of  the  cerebrum  over  the  spinal  functions, 
although  there  is  probably  some  more  direct  efferent  relation  between  the 
efferent  cerebellar  impulses  and  the  spinal  functions  through  the  vestibulo- 
spinal tract,  that  there  constantly  leave  the  cerebellum  a  flow  of  efferent 
impulses  which  provide  for  the  most  efficient  co-ordination  of  individual  muscles 
during  either  states  of  rest  or  activity;  and  also,  through  chiefly  the  extero- 
ception  impulses  of  static  sensation,  the  maintaining  of  the  best  balanced  posi- 
tion of  the  center  of  gravity  of  the  whole  body. 

438 


-Yiw^X^^^^. 


^'^a.^.^v.'^^^    vt,^ 


>iri-!l-^  ...*«-  W  AJ,^      /?^. 


THE  NERVOUS  SYSTEM 
/ 
/  Page  360 

Q.  Describe  the  histology  of  the  cerebellar  cortex. 

A.  The  characteristic  cell  of  the  cerebellum  is  the  cell  of  Pur  kin  je.  It 
is  flask  shaped  and  from  its  apex  a  rich  turf  of  dendrites  arise.  Its  axon 
arises  from  the  base  of  the  cell  and  passes  into  the  white  substance  of  the 
cerebellum  to  the  central  nuclei.  This  cell  lies  between  two  layers  of  smaller 
cells,  the  dendrites  and  axons  of  which  are  chiefly  associative  in  function. 

Page  362 

Q.  What  are  the  symptoms  of  the  cerebellarless  animal? 
A.  Asthenia,  atonia  and  astasia.     See  text  for  definition. 

Page  368 

Q.  What  is  the  characteristic  of  cerebellar  ataxia,  and  how  does  it  differ 
from  the  two  types  of  spinal  ataxia? 

A.  A  failure  to  maintain  the  normal  position  of  the  center  of  gravity 
of  the  body.  It  might  be  described  as  a  top-heavy  ataxia,  exactly  analogous 
to  the  ataxia  of  a  drunken  individual.  It  differs  from  the  spinal  ataxia  of 
lateral  sclerosis,  in  which  the  pyramidal  tracts  are  degenerated,  in  that  in 
the  latter  all  movements  are  exaggerated;  the  ataxia  is  due  to  over-movement. 
It  differs  from  spinal  ataxia  of  tabes  dorsalis,  in  which  the  posterior  columns 
of  Goll  and  Burdach  are  degenerated,  in  that  in  tabes  the  ataxia  is  character- 
ized by  an  inexactness  of  all  movements  depending  upon  a  blunting  of  the 
sensations  informatory  of  the  exact  position  of  individual  muscles  and  tendons 
and  joints. 

Page  370 

Q.  What  additional  possibilities  of  action  does  the  possession  of  the  cere- 
bral hemispheres  afford  an  animal? 

A.  That  alteration  of  activity  which  depends  upon  memory.  In  the 
animal  deprived  of  its  cerebral  hemispheres  the  nervous  path  between  the 
incoming  sensory  impulses  and  action  is  so  direct  that  these  animals  respond 
to  external  stimulation  with  a  machine-like  certainty. 

An  animal  with  a  cerebral  hemisphere  responds  in  an  uncertain  manner, 
because  of  the  influence  of  impulses  along  many  association  tracts  which 
have  been  brought  into  relation  with  incoming  stimuli  by  past  experiences. 
In  virtue  of  these  intervening  impulses  between  sensation  and  action  a  deport- 
ment results  which,  according  to  the  function  of  the  action,  is  classified  as  an 
expression  of  all  the  higher  possibilities  of  which  the  mind  is  capable,  such  as 
love,  fear,  self-restraint,  etc. 

Page  372 

Q.  What  region   of  the  cerebral   cortex  is  the   so   to   speak  terminal  dis- 
charging station  of  motion? 
A.  See  text. 

Page  378 

Q.  What  is  the  distinguishing  characteristic  of  movements  excited  by 
stimulation   of   the  cerebral   cortex? 

A.  Their  similarity  to  the  voluntary  movements  of  the  animal,  involving 
such  a  co-ordination  of  inhibition  and  contraction  that  the  movement  becomes 
purposeful  in  the  highest  sense. 

440 


f 


THE  NERVOUS  SYSTEM 

Tage  S80 

Q.  What  is  the  difference  in  the  character  of  the  control  exercised  over 
voluntary  movement  by  the  cerebrum  and  cerebellum? 

A.  The  cerebrum  initiates  motion  and  determines  what  muscles  shall  be 
called  into  play  in  the  accomplishment  of  a  definite  movement  or  combinations 
of  motion,  vphile  the  cerebellum  controls  the  varying  degree  of  contraction  and 
relaxation  of  muscles  only  so  far  as  is  necessary  for  the  accomplishment  of 
perfect  co-ordination  and  maintenance  of  the  correct  position  of  the  center 
of  gravity  of  the  body  during  the  progression  of  these  niovements  or  the  inter- 
vening states  of  muscular  contraction. 

Page  384 

Q.  What  area  of  the  cortex  is  associated  with  the  reception  of  sensations 
of  muscular  sensations  of  touch,  temperature  and  pain? 

A.  Tactile  sensation  of  touch  and  muscular  sensations  are  received  first 
by  the  cells  of  the  ascending  parietal  convolution  immediately  posterior  to 
the  fissure  of  Eolando,  the  inferior  parietal  and  supramarginal  convolutions. 

Sensations  of  pain  are  received  by  cells  fairly  widely  distributed  in  the 
cortex.  The  location  has  not  been  exactly  identified.  Those  cells  receiving 
the  sensations  of  temperature  have  not  been  definitely  located,  but  they  prob- 
ably occupy  areas  common  to  the  cells  receiving  cutaneous  sensibility. 


Page  386 

Q.  What  areas  in  the  cortex  receive  visual  sensations? 
A.  The  cortex  of  the  occipital  lobes. 

Page  388 


Q.  What  area  in  the  cortex  receives  auditory  sensations? 

A.  The  cortex  of  the  superior  temporal  convolution;  but  there  is  evidence 
that  this  region  is  not  the  only  one  devoted  to  the  reception  of  auditory 
sensations,  and  that  other  more  widely  distributed  areas  also  participate 
in  this  function,  though  their  exact  location  is  as  yet  unidentified. 

Q.  What  areas  in  the  cortex  receive  sensations  of  smell  and  taste? 

A.  Many  portions  of  the  limbic  lobe,  including  particularly  the  inferior 
surface  of  the  frontal  lobe,  the  portion  of  limbic  lobe  contiguous  to  the  corpus 
callosum,  the  uncus  and  the  hippocampus  major. 

Page  390 

Q.  What  is  the  function  of  the  large  areas  of  the  cortex  intervening 
between  sensory  and   motor  areas  described? 

A.  These  so-called  silent  areas  perform  association  functions.  By  them 
the  primary  sensations  are  grouped  into  concepts,  and  the  concepts  themselves 
are  compounded  and  compared  with  otlier  similar  concepts,  suggested  because 
of  their  analogy  by  them  and  the  cerebral  states  depending  upon  this  variety 
of  concepts,  stimulated  so  that  the  rudiments  of  tlie  higher  faculties  of  choice 
and  judgment  and  decision  are  possible.  These  highest  faculties  are  performed 
by  the  frontal  portions  of  the  cortex. 

442 


THE  NERVOUS  SYSTEM 

Page  392 

Q.  How  may  words  be  psychologically  defined,  and  how  do  they  facilitate 
cerebral  processes? 

A.  Words  are  names  given  by  the  mind  to  concepts  of  varying  complexity, 
and  by  the  use  of  these  symbols  for  complex  cerebral  process,  the  cerebral 
states  involved  in  concepts  of  extreme  complexity  may  be  quickly  produced, 
and  thus  Intricate  thinking  facilitated  or  made  possible. 

Fage  394 

Q.  What  is  aphasia,  how  many  kinds  of  aphasia  are  there,  and  to  what 
are  they  due? 

A.  Aphasia  is  an  impairment  in  the  power  of  speech.  It  may  be  an 
anarthria,  due  to  a  pure  inability  to  phonate. 

It  may  be  a  motor  aphasia,  due  to  an  inability  to  associate  or  select 
the  proper  words  to  express  properly  formed  concepts. 

It  may  be  sensory,  due  to  the  inability  to  associate  with  the  name  of  a 
concept  its  proper  sound  as  heard  or  form  as  written. 

Page  400 

Q,  Where  is  the  thermotaxic  center  of  the  body  situated? 
A,  Probably  in  the  corpus  striatum.     See  text. 

Q.  Describe  the  histology  of  the  cerebral  cortex? 

A.  The  pyramidal  shaped  cell,  with  apical  and  lateral  dendrites  and  basal 
axon,  is  the  typical  cerebral  cell.  It  is  disposed  in  several  layers  composed 
of  pyramidal  cells  of  different  size,  and  is  entirely  associative  in  function. 
In  addition  to  these  cells  there  are  other  layers  of  differently  shaped  cells, 
superficial  and  deeper  to  them,  and  all  layers  are  separated  or  crossed  by 
strata  of  fibers.  The  thickness  of  both  layers  of  cells  and  of  fibers  differs 
according  to  the  functions  of  different  portions  of  the  cerebral  cortex. 

Page  406 

Q.  What  is  the  vegetative  nervous  system,  and  into  how  many  portions  is 
it  divided? 

A,  In  general  that  system  the  nerves  of  which  supply  the  involuntary 
muscles.  It  is  divided  into  the  cranial  or  autonomic,  and  the  spinal  or 
sympathetic  portions. 

Q.  What  cranial  nerves  contain  fibers  of  the  vegetative  nervous  system, 
and  what  do  these  nerves  supply? 

A.  The  third  cranial,  the  vegetative  nerves  of  which  supply  the  sphincter 
pupili  and  the  ciliary  muscle. 

The  seventh  nerve,  the  vegetative  nerves  of  which  supply  the  sublingual 
and  submaxillary  glands  with  secretory  and  vasodilator  nerves  to  the  parotid 
gland. 

The  tenth  is  entirely  vegetative.  It  supplies  motor  impulses  to  the 
alimentary  tract  as  far  as  the  ileocolical  valve,  inhibitory  impulses  to  the 
heart,  motor  impulses  to  the  bronchi,  and  secretory  fibers  to  the  stomach 
and  pancreas.     It  contains  afferent  fibers,  passing  to  the  important  medullary 

444 


THE  NERVOUS  SYSTEM 

centers,  and  through  which  the  heart  beat  is  slowed  and  respiration  is  quick- 
ened and  the  blood  pressure  lowered. 

Q.  Describe  the  anatomy  and  ganglia  of  the  spinal  sympathetic  nerves. 
A.  See  text. 

Page  414 

Q.  What  are  the  connections  and  functions  of  the  superior  cervical  sym- 
pathetic ganglia? 
A.  See  text. 

Q,  What  are  the  functions  of  the  first  five  dorsal  nerves  making  connec- 
tions with  the  cervical  and  stellate  ganglia? 
A.  See  text. 

Q.  What  sympathetic  nerves  supply  the  upper  limbs  and  what  are  their 
functions? 

A.  See  text. 

Q.  What  sympathetic  norves  supply  the  lower  limbs,   and  what  is  their 
function? 

A.  See  text. 

Q.  What  is  the  nerve  supply  of  the  pelvic  plexus,  and  the  function  ful- 
filled by  them? 
A.  See  text. 

Q.  What  nerves  form  the  nervi  erigentes,  and  what  is  their  function? 
A.  See  text. 


Paul  B.  Hoeber,  67-69  East  59th  Street,  New  York 
446 


LECTURE    NOTES 

ON 

PHYSIOLOGY 


BY 


HENRY  H.  JANEWAY,  M.D. 


STRUCTURAL  AND  CHEMICAL  UNITS 
OF  THE  BODY 


NEW    YORK 

PAUL    B.    HOEBER 

67-69  EAST  59th  STREET 


Copyright,  1915, 
By  PAUL  B.  HOEBER 


STRUCTURAL  AND  CHEMICAL 
UNITS  OF  THE  BODY 

The  Structural  Units  of  the  Body — The  structural  unit  of  any 
living  plant  or  animal  is  the  cell,  and  the  functions  of  the  body 
are  the  sum  of  the  functions  of  all  the  cells  of  the  body. 

The  Law  of  Recapitulation — Every  highly  organized  animal 
has  developed  from  one  cell  by  a  process  of  division,  growth  and 


Fig.  1. — General  view  of  cells  m  the  growing  root-tip  of  the  onion,  from  a  longi- 
tudinal section,  enlarged  800  diameters.     (Wilson.) 

a.  Non-dividing  ceUs,.  with  chromatin-network  and  deeply  stained  nucleoli; 
b.  nuclei  preparing  for  division  (spireme-stage) ;  c.  dividing  cells  showing 
mitotic  figures;  e.  pair  of  daughter-ceUs  shortly  after  division. 

differentiation  of  the  descendants  of  this  single  cell.  In  this  proc- 
ess of  division,  growth  and  differentiation  there  may  be  recognized 
the  morphology  of  simpler  organized  animals  which  represent  the 
stages  by  which  the  more  highly  organized  animals,  including  man 
himself,  have  been  developed  from  the  simpler  forms  of  life. 
The  Description  of  the   Cell — In  the   stems   of  plants  cells 

2 


m' 
% 


K  :.'^ 


.     STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

appear  as  hollow  sacs  composed  of  a  strong  cell  wall  of  cellulose 
lined  internally  by  a  thin  layer  of  protoplasm  which  really  con- 
stitutes the  cell  body  and  is  termed  the  primordial  utricle.  The 
latter  contains  at  one  point  a  nucleus  and  the  sac  surrounded  by  it 
is  filled  with  cell  sap.  In  the  growing  tips  of  plants  the  nucleus  is 
large  and  occupies  a  central  position  and  a  protoplasmic  cell  body 
fills  the  entire  space  inclosed  by  the  cell  wall.     (See  Fig,  1.) 

Unicellular  Animals  as  Types  of  Cells — As  a  type  of  the  an- 


Fig.  2. — Amoeba  Proteus,  an  animal  consisting  of  a  single  naked  cell.     X  280. 
(Wilson.) 

n.  The    nucleus;    w.v.  water- vacuoles;   c.v.  contractile  vacuole;   f.v.  food- 
vacuole. 

imal  cell  in  general  the  unicellular  organism  is  the  best  repre- 
sentative and  no  form  of  cell  serves  this  purpose  better  than  the 
ameba. 

It  may  be  found  in  stagnant  pools  of  water  and  appears  as  a 
simple  mass  of  protoplasm  about  0.1  to  .3  mm.  in  diameter.  When 
examined  under  the  microscope  there  may  be  distinguished  (see 
Fig.  2)— 

1.  A  clear  external  zone  around  the  whole  periphery  of  the 
cell  and  within  this  the  granular  protoplasm  or  substance  of  the 
cell  body. 

2.  The  nucleus,  a  spherical,  more  highly  refractile  and  darker 
body. 

4 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 


3.  Contractile  vacuole,  another  spherical  body  but  clear,  which 
is  apparently  filled  with  fluid  and  undergoes  rhythmic  contrac- 
tions. These  contractions  serve  to  keep  up  a  circulation  within 
the  cell  body. 

4.  Other  clear  but  smaller  vacuoles  which  are  not  contractile 
are  also  found  within  the  cells.    These  are  called  water  vacuoles. 

5.  There  may  also  be  found  particles  of  food  in  various  stages 
of  digestion  within  the  cell. 

Power  of  Movement  of  the  Animal  Cell — Power  of  movement 
is  possessed  by  the  ameba  and  is  accomplished  by  protruding 
from  its  self  finger-like  projections  of  its  protoplasm  called 
pseudopodia. 

Protoplasm — The  protoplasm  of  which  all  cells  consist  may 
be  defined  as  the  physical  basis  of  life.  It  is  not  a  single  sub- 
stance nor  is  there  one  protoplasm.  Every  varying  function  of 
different  cells  or  of  the  same  cell  is  performed  by  a  different 
kind  of  protoplasm. 

THE    STRUCTURE    OF    A    CELL 

The  Parts  of  the  Cell  Body  or  of  the  Cytoplasm — Every  cell 
consists  of  a  cell  body  and  a  nucleus.  The  parts  of  the  cell  body 
are  (see  Fig.  3)  :  deb 


Fig.  3. — Diagram  of  a  cell.  Its  basis  consists  of  a  mesh  work  containing  numerous 
minute  granules  (microsomes)  and  traversing  a  transparent  ground-substance, 
a — nucleolus;  b — chromatorie;  c — phyrin  of  linin  or  nucleoreticulum ;  d — pseudo 
nucleoli  or  nodal  thickening  of  the  chromatin  at  intersection  joints;  e — vac- 
uole; f — food  particles;  g — plastids;  h — centrosome. 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

1.  Cell  Wall — The  cell  wall  is  not  always  present.  In  plants 
it  is  cellulose.  In  many  animals  it  is  calcareous.  So  far  as  the 
life  of  the  cell  is  concerned  it  may  be  considered  protective  only; 
around  cells  of  many  animals  the  intercellular  substance  corre- 
sponds to  the  cell  wall.     (See  Fig.  4.) 

2.  Plasmahaut — Within  the  wall  or  lying  next  to  the  inter- 
cellular substance  is  the  true  boundary  of  the  cell.    It  is  called  the 


■Mi'fi* 


^ 


^ 


'^m  V. 


Fig.  4. — A  portion  of  the  epidermis  of  a  larval  salamander  [Amblystoma)  as  seen 
in  slightly  obhque  horizontal  section,  enlarged  550  diameters.  Most  of  thecells 
are  polygonal  in  form,  contain  large  nuclei,  and  are  connected  by  delicate 
protoplasmic  bridges.  Above  x  is  a  branched,  dark  pigment-cell  that  has 
crept  up  from  the  deeper  layers  and  hes  between  the  epidermal  cells.  Three  of 
the  latter  are  undergoing  division,  the  earliest  stage  {spireme)  at  a,  a  later  stage 
(mitotic  figure  in  the  anaphase)  at  h,  showing  the  chromosomes,  and  a  final 
stage  (telophase),  showing  fission  of  the  cell  body,  to  the  right. 

plasmahaut  and  consists  of  a  layer  of  protoplasm  different  in  its 
chemical  composition  and  concentration  from  the  remaining  por- 
tions of  the  protoplasm. 

3.    Cell  Protoplasm — the  Cytoplasm — Within  the  plasmahaut  is 
the  protoplasm  proper  consisting  of  two  portions: 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

a  A  fine  network  tlirougliout  the  cell  known  as  the  spongio- 
plasm. 

&  A  semisolid  more  or  less  granular  or  sometimes  even  homo- 
geneous substance  filling  the  meshwork  of  the  spongioplasm  termed 
hyaloplasm.  The  network  or  spongioplasm  and  hyaloplasm  to- 
gether constitute  the  cytoplasm. 

c  Contained  within  the  cytoplasm  are  many  granules  and 
some  of  larger  size  called  plastids.  The  latter  are  identified 
with  the  various  functions  of  the  cell  body.  In  plant  cells  some 
of  them  are  called  chloroplasts  because  they  contain  chlorophyl 
and  are  concerned  in  the  formation  of  sugar  out  of  the  carbon 
dioxide  of  the  atmosphere.  Others  are  called  leucoplasts.  They 
transform  sugar  into  starch. 

d  The  cytoplasm  may  contain  clear  water  vacuoles.  In  some 
cells  one  or  two  of  these  may  possess  the  power  of  contraction  and 
are  then  called  contractile  vacuoles. 

e  Another  body  of  considerable  importance  in  connection  with 
cell  division  is  the  centrosome.  It  consists  of  a  central  highly 
refractile  and  dark  staining  dot,  the  centriole ;  around  this  a 
clear  area,  the  attraction  sphere ;  and  surrounding  the  attraction 
sphere  an  area  characterized  by  radiating  lines  throughout  the 
protoplasm  for  a  greater  distance,  the  archoplasm. 

4.  Nucleus — In  every  cell  there  is  found  a  nucleus  which  is 
inclosed  within  its  own  membrane.  The  nuclear  membrane  is  com- 
posed of  a  substance  called  amphipyrenin.  Within  this  membrane 
is  a  nuclear  network  called  nueleoreticulum,  composed  of  a  sub- 
stance called  linin.  Upon  this  network  are  strung  granules  or 
short  rods  (depending  upon  the  stage  of  cell  life)  called  chromatin. 
Within  the  nucleus  is  a  still  smaller  and  more  deeply  staining  body 
called  the  nucleolus.  The  nucleolus  is  composed  of  a  substance 
called  pyrenin. 

Between  the  meshwork  of  the  nueleoreticulum  is  contained 
the  nuclear  sap,  the  nucleoplasm ;  it  corresponds  to  the  hyaloplasm 
of  the  cytoplasm.  The  name  false  nucleoli  is  applied  to  the  darker 
staining  intersections  of  the  nuclear  network. 

The  Units  of  Functional  Activity  of  Cells — A  number  of 
theories  have  been  formulated  in  attempts  to  identify  the  mor- 
phological units  producing  the  granular  appearance  of  protoplasm 
with  units  of  functional  activity  of  the  cell.     According  to  one 

io 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

of  these  theories  the  functional  units  are  the  granules  of  the 
protoplasm.;  according  to  another  the  fluid  contained  within  the 
fibrillar-like  structure,  and  according  to  a  third  the  alveolar-like 
structure  separated  only  by  contiguous  surfaces  are  the  units 
of  functional  activity.  None  of  these  theories,  however,  must  be 
taken  too  seriously  inasmuch  as  the  morphological  differentiation 
upon  which  they  are  based  may  in  part  be  produced  artificially 
and  is  not  constantly  present  in  all  cells. 

Some  of  the  Characters  of  the  Protoplasm  of  a  Cell — It  is 
necessary  to  formulate  a  clear  conception  of  protoplasm.  The 
rapid  streaming  movements  seen  in  the  protoplasm  of  the  ameba 
and  of  many  other  cells  indicates  that  it  is  in  the  first  place  fluid. 
Its  failure  to  mix  with  the  surrounding  media  in  which  the  cell  is 
immersed  is  to  be  explained  by  two  facts,  first,  that  it  is  of  a 
different  composition  and,  second,  that  it  possesses  a  superficial 
layer  of  at  least  a  different  concentration  and  sometimes  of  a 
different  chemical  composition. 

A  greater  concentration  of  the  surface  layers  is  a  property 
of  all  colloidal  fluids. 

The  Functions  of  the  Plasmahaut  and  Its  Adaptation  to  this 
Function — The  resistance  of  cells  to  deformation  may  be  entirely 
accounted  for  by  the  fact  that  there  is  a  greater  concentration  of 
the  superficial  layer  which  imparts  to  it  an  increased  surface 
tension. 

It  is  entirely  by  means  of  the  surface  layer  of  any  cell  that 
it  comes  into  relation  with  its  environment.  The  nature  of  this 
layer  called  the  plasmahaut  is  of  first  importance  to  the  life  of 
the  cell. 

Upon  the  varying  degrees  of  solubility  in  this  layer  of  the  sub- 
stances serving  the  cell  as  food  depends  in  part  the  nutrition  of  the 
cell  as  well  as  the  shape  of  the  cell. 

Apart  from  the  greater  concentration  of  the  colloidal  materials 
in  the  surface  layer  of  a  cell,  all  substances  with  which  the  cell 
usually  comes  into  contact  are  only  limitedly  soluble  in  this  sur- 
face layer.  It  is  freely  permeable  to  water  but  not  to  salts,  sugars 
and  amino-acids.  It  easily  permits  the  passage  of  alcohols,  alde- 
hydes and  alkaloids. 

Tp  substances,  however,  to  which  the  plasmahaut  is  relatively 
impermeable  it  is  often  slightly  permeable,  and  two  factors  make 

12 


STEUGTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY' 

it  possible  for  relatively  krge  amounts  of  such  substances  to  pass 
through  it.  One  is  the  possibility  of  the  substance  being  rapidly 
removed  as  a  result  of  transformation  after  its  entrance  into  the 
cell.  The  second  is  the  possibility  of  changes  in  the  plasmahaut 
wrought  as  a  result  of  the  activity  in  the  cell  itself. 

The  Vital  Phenomena  of  Cells — The  following  are  the?  vital 
phenomena  common  to  all  cells: 

1.  Assimilation — It  includes  three  processes:  the  ingestion  of 
food,  its  digestion,  and  its  retransformation  into  its  own  proto- 
plasm or  into  substances  useful  to  the  living  activities  of  the  cell. 
By  digestion  is  meant  the  transformation  of  the  food  ingested,  in 
a  form  available  for  the  life  of  the  cell,  into  a  form  from  which 
the  cell  can  manufacture  its  own  protoplasm. 

The  form  in  which  food  is  ingested  and  the  substances  into 
which  it  is  transformed  are  quite  different  for  both  plants  and 
animals. 

Within  plants  assimilation  is  far  more  completely  synthetic 
than  is  the  case  with  animals.  The  former  take  in  all  substances 
in  simple  forms,  build  them  up  into  complex  bodies  and  as  these 
store  up  the  sun's  energy  in  a  potential  form. 

While  animals  take  in  their  food  stuffs  in  combinations  of 
a  complex  form  and  break  these  up,  they  yet  display  con- 
structive assimilation  by  reforming  the  broken  down  units  into  the 
peculiar  complex  compounds  needed  for  their  own  use. 

2.  Dissimilation — Each  cell  performs  the  various  functions  in- 
cidental to  its  life  at  the  expense  of  energy.  This  energy  is  derived 
from  the  oxidation  of  complex  incompletely  oxidized  combinations 
of  carbon  formed  by  the  processes  of  assimilation.  All  these 
changes  occurring  within  the  cell  by  which  not  only  the  complex 
molecules  ingested  within  it  are  taken  apart  for  the  purpose  of 
re-formation  or  after  re-formation  are  again  taken  apart  for  the 
purpose  of  yielding  energy,  or  after  having  been  partially  broken 
down  in  the  production  of  energy  or  in  consequence  of  the  vital 
activities  of  the  cell  are  further  taken  apart  and  prepared  for  ex- 
cretion from  the  cell — all  are  included  in  the  term  dissimilation. 

The  nitrogenous  compounds  are  chiefly  eliminated  as  urea,  the 
carbon  as  carbonates  and  carbon  dioxide  and  the  other  elements  as 
inorganic  salts. 

^,     Excitability — Every  living  cell  is  capable  of  responding  to 

14 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

changes  iu  its  external  environment  by  a  series  of  dissimilatory 
changes,  representing  a  discharge  of  energy. 

These  changes  in  the  environment  of  a  cell  are  called  stimuli. 
They  may  be  changes  in  resistance  to  the  external  forces  in  con- 
tact with  a  cell.  Such  changes  are  iUustrated  by  touch  stimuli  and 
the  response  to  them  is  called  thigmotaxis. 

They  may  be  changes  toward  differences  of  light  in  which  case 
the  response  is  called  phototaxis.  They  may  represent  a  response 
to  gravity  called  geotaxis.  A  response  to  chemical  stimuli  is  called 
chemotaxis. 

A  characteristic  of  excitability  is  that  the  response  is  or  may 
be  far  in  excess  of  the  force  represented  by  the  stimulus. 

4.  Contractility — All  cells  possess  the  power  of  movement 
though  it  may  only  be  intracellular  in  the  case  of  some  cells.  Illus- 
trations of  the  ameba's  power  of  movement  have  already  been 
given. 

5.  Adaptability — All  cells  possess  the  power  of  adaptability. 
Were  it  not  for  the  fact  that  the  first  forms  of  life  were  endowed 
with  this  quality  there  would  have  been  no  possibility  of  life  hav- 
ing survived  all  the  cosmic  changes  through  which  it  has  passed 
in  its  development  from  the  simplest  forms  to  the  complicated 
human  being. 

Adaptability  Has  Its  Limits — No  life  can  continue,  in  spite  of 
adaptability,  in  the  lack  of  food  supply  furnished  in  an  assimi- 
latable  form  or  in  the  lack  of  water  or  in  the  presence  of  extremes 
of  temperature;  no  life  can  exist  in  a  temperature  below  0°  C.  or 
above  50°  C. 

6.  Growth  and  Reproduction — The  two  processes  of  assimila- 
tion and  dissimilation  proceed  together  in  every  cell.  If  assimila- 
tion is  in  excess,  the  living  body  increases  in  size,  when  the  dis- 
similatory changes  exceed  the  assimilatory  changes  death  occurs. 
Growth  and  reproduction  are  phenomena  common  to  all  life.  They 
are  ubiquitously  illustrated  by  all  the  simple  forms  of  life. 

Subtracting  the  increase  of  weight  due  to  growth  and  repro- 
duction the  products  of  dissimilation  are  equal  to  those  of  assimila- 
tion. The  law  of  the  conservation  of  energy  holds  true  in  the  realm 
of  life  as  well  as  in  that  of  cosmic  changes.  Exact  experiments 
upon  animal  life,  and  upon  man  himself,  show  that  the  combined 
output  of  energy  measured  as  heat  plus  the  incompletely  oxidized 

16 


^  (^-.  c=  a 


^A  ^ 


If 


^1 


n+e)"^ 


-V"~l^' 


STRUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

products  excreted  equal  exactly  the  intake  caloric  value  of  the 
food. 

In  the  process  of  reproduction  the  nucleus  plays  a  most  impor- 
tant part.  Cell  division  may  occur  by  amitosis  or  by  karyo- 
kinesis. 

Cell  Division — Cell  division  by  amitosis  is  the  simpler. 
A  cell  about  to  divide  in  this  manner  simply  becomes  constricted 
at  its  middle.     This  change  follows  a  similar  constriction  in  the 


Fig.  5. — Group  of  cells  with  amitotically  dividing  nuclei;  ovarian  follicular  ep- 
ithelium of  the  cockroach.      (Wilson.) 


nucleus.  The  constriction  deepens  in  each  until  two  cells  result. 
(See  Fig.  5.) 

The  usual  manner  in  which  cells  divide  is  by  karyokinesis.  In 
this  form  very  complicated  changes  occur  in  the  nucleus  which 
have  for  their  object  an  equal  distribution  of  the  chromatic  sub- 
stances of  the  nucleus  to  each  daughter  cell.  The  process  includes 
four  phases  (see  Figs.  6,  7,  8  and  9)  :  • 

1.  Prophase — (a)  The  chromatic  substance  forms  a  long 
spireme  thread,  winding  throughout  the  nucleus.  The  thread 
thickens  and  shortens  and  there  is  a  disappearance  of  the  nuclear 
membrane.     The  spireme  thread  breaks  up  into  segments  which 

18 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 


approach  the  equatorial  plane  of  the  cell.  (&)  While  this  is  pro- 
ceeding the  centrosome  divides  and  each  half  begins  to  travel 
toward  the  opposite  poles  of  the  cell.  Delicate  radiating  lines, 
forming  the  achromatic  spindle,  appear  between  the  daughter 
centrosomes. 


Fig.  6. ^-Diagrams  showing  the  prophases  of  mitosis.     (Wilson.) 

A.  Resting  cell  with  reticular  nucleus  and  true  nucleolus;  at  c  the  attraction- 
sphere  containing  two  centrosomes.  B.  Early  prophase;  the  chromatin  form- 
ing a  continuous  spireme,  nucleolus  still  present;  above,  the  amphiaste'r  (a). 
CD.  Two  different  types  of  later  prophases.  C.  IDisappearance  of  the  primary 
spindle,  divergence  of  the  centrosomes  to  opposite  poles  of  the  nucleus  (examples, 
some  plant-cells,  cleavage-stages  of  many  eggs).  D.  Persistence  of  the  primary 
spindle  (to  form  in  some  cases  the  "central-spindle"),  fading  of  the  nuclear 
membrane,  in  growth  of  the  astral  rays^  segmentation  of  the  spireme-thread 
to  form  the  chromosomes  (examples,  epidermal  cells  of  salamander,  formation 
of  the  polar  bodies).  E.  Later  prophase  of  type  C;  fading  of  the  nuclear  mem- 
brane at  the  poles,  formation  of  a  new  spindle  inside  the  nucleus;  precocious 
splitting  of  the  chromosomes  (the  latter  not  characteristic  of  this  type  alone). 
F.  The  mitotic  figure  established;  e.p.  the  equatorial  plate  of  chromosomes. 

20 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

2.  Metaphase — The  centrosomes  reach  the  opposite  poles  and 
the  polar  radiations  between  them  are  more  apparent. 

There  is  a  definite  arrangement  of  the  chromatic  filaments  in 
V-shaped  loops  in  the  equatorial  plane  of  the  cell. 

The  apex  of  each  V  is  directed  toward  the  center  of  this  plane. 


C  D 

Fig.  7. — The  prophases  of  mitosis  (heterotypical  form)  in  primary  spermatocytes 
of  Salamandra.     (Wilson.) 

A.  Early  segmented  spireme;  two  centrosomes  outside  the  nucleus  in  the 
remains  of  the  attraction-sphere.  B.  Longitudinal  splitting  of  the  spireme, 
appearance  of  the  astral  rays,  disintegration  of  the  sphere.  C.  Early  amphi- 
aster  and  central  spindle.  D.  Chromosomes  in  the  form  of  rings,  nuclear  mem- 
brane disappeared,  amphiaster  enlarging,  mantle-fibres  developing. 

The  whole  gives  the  appearance  of  a  star.  Hence  this  appearance 
is  called  the  monaster.  Each  V-shaped  loop  now  splits  longitudi- 
nally and  the  two  halves  begin  to  separate  upon  a  thread  of  the 
polar  radiation  toward  the  pole  of  the  cell.     The  point  of  the  V 

22 


STEUCTURAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

travels  first.    This  appearance  resembles  a  double  star  and  is  called 
the  diaster. 

3.    The  Anaphase — Each  half  chromosome  or  split  V-shaped 
segment  travels  to  the  extremity  of  the  polar  spindle. 


F  ^ 

Fig.  8. — Metaphase  and  anaphases  of  mitosis  in  cells  (spermatocytes)  of  the  sala- 
mander.    (Wilson.) 

E.  Metaphase.  The  continuous  central  spindle  fibres  pass  from  pole  to 
pole  of  the  spindle.  Outside  them  the  thin  layer  of  contractile  mantle-fibres 
attached  to  the  divided  chromosomes,  of  which  only  two  are  shown.  Centro- 
somes  and  asters.  F.  Transverse  section  through  the  mitotic  figure  showing 
the  ring  of  chromosomes  surrounding  the  central  spindle,  the  cut  fibres  of  the 
latter  appearing  as  dots.  G.  Anaphase;  divergence  of  the  daughter-chromo- 
somes, exposing  the  central  spindle  as  the  interzonal  fibres;  contractile  fibres 
(principal  cones  of  Van  Beneden)  clearly  shown.  H.  Later  anaphase  (diaster 
of  Flemming);  the  central  spindle  fully  exposed  to  view;  mantle-fibres  attached 
to  the  chromosomes.     Immediately  afterward  the  cell  divides. 


The  body  of  the  cell  is  constricted  in  the  same  equatorial  plane. 
The  constriction  proceeds  until  two  daughter  cells  result. 

4.    Telophase — In  inverse  order  the  above  changes  are  repeated 

24 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

until  two  new  cells  are  formed  each  with  a  new  nucleus  possessing 
a  new  nuclear  membrane  and  new  chromatic  granules. 

7.  Metakinesis — It  must  be  assumed  that  there  is  in  every  cell 
that  force  which  later  develops  in  the  human  into  consciousness. 
To  this  hypothetical  potential  consciousness  Lloyd  Morgan  has  ap- 
plied the  term  metakinesis,  though  this  term  is  also  used  in  another 


nX- 


c 


r 


x> 


Fig.  9. — Mitosis  in  Stypocaulon.     (Wilson.) 

A.  Early  prophase  with  single  aster  and  centrosome.  B.  Initial  formation 
of  intranuclear  spindle.  C.  Divergence  of  the  daughter-centrosomes,  D.  Early 
anaphase;  nuclear  membrane  stiU  intact. 

sense  to  designate  the  phases  of  cell  division  succeeding  the  sepa- 
ration of  the  two  daughter  cells. 

There  are  no  manifestations  of  its  existence  in  the  first  sense 
in  the  primitive  cell. 

8.  Conduction — All  cells  possess  the  power  of  transmitting 
across  them  molecular  changes  due  to  stimuli  applied  to  one  point 
on  their  surfaces. 

The  whole  nervous  system  of  highly  developed  forms  of  life 
represents  cells  apart  for  the  special  performance  of  this  function. 

9.  Organization — Though  not  a  phenomenon,  organization  will 

26 


STEUCTUKAL  AND  CHEMICAL  UNITS  OF  THE  BODY 

be  mentioned  here  because  this  is  an  important  characteristic  of 
all  cells.  It  becomes  more  and  more  marked  as  function  becomes 
more  and  more  specialized.  So  true  is  this  fact  that  one  may 
almost  say  that  structure  is  the  determining  factor  of  function. 


C^5x    (^ 


^ 


//^ 


B 


^ 


^       D 


Fig.  10. — Nucleated  and  non-nucleated  fragments  of  Ameha.     (Wilson.) 

A.B.  An  ameba  divided  into  nucleated  and  non-nucleated  halves,  five 
minutes  after  the  operation.  CD.  The  two  halves  after  eight  days,  each 
containing  a  contractile  vacuole. 

* 

We  may  at  least  claim  that  with  greater  efficiency  of  function 

there  is  required  greater  complexity  of  structure. 

The  Relation  of  the  Nucleus  to  the  Cytoplasm — Many  facts 
demonstrate  that  the  nucleus  performs  very  special  functions  in 
the  life  of  the  cell;  functions  quite  different  and  of  more  vital 
importance  than  those  of  the  cytoplasm. 

28 


STRUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 


B  C 

Fig.  11. — Regeneration  in  the  unicellular  animal  Stentor.     (Wilson.) 

A.  Animal  divided  into  three  pieces,  each  containing  a  fragment  of  the  nu- 
cleus. B.  The  three  fragments  shortly  afterward.  C.  The  three  fragments 
after  twenty-four  hours,  each  regenerated  to  a  perfect  animal. 


Fig.  12. — Stylonychia,  and  enucleated  fragments.     (Wilson.) 

Below  is  an  entire  animal,  showing  planes  of  section.  The  middle  piece, 
containing  two  nuclei,  regenerates  a  perfect  animal.  The  enucleated  pieces, 
shown  above,  swim  about  for  a  time,  but  finally  perish. 

30 


STEUCTUEAIi  AND  CHEMICAL  UNITS  OF  THE  BODY 

1.  In  the  process  of  cell  division  there  is  the  most  careful 
provision  for  an  equal  distribution  of  nuclear  material  in  the  two 
daughter  cells. 

2.  No  cell  can  maintain  a  continued  existence  in  the  absence 


A 


C 


D 


Fig.  13. — Formation  of  membranes  by  protoplasmic  fragments  of  plasmolyzed 
cells.     (Wilson.) 

A.  Plasmolyzed  cell,  leaf -hair  of  cucurbita,  showing  protoplasmic  balls  con- 
nected by  strands.  B.  Calyx-hatr  of  Gaillardia;  nucleated  fragment  with 
membrane,  non-nucleated  one  naked.  C.  Root  hair  of  Marchantia;  all  the 
fragments,  connected  by  protoplasmic  strands,  have  formed  membranes.  D. 
liBaf-hair  of  Cucurbita;  non-nucleated  fragment,  with  membrane,  connected 
with  nucleated  fragment  of  adjoining  cell. 


of  a  nucleus.  By  various  means,  plasmolysis,  violent  shaking  or 
Ijy  direct  dissection,  cells  may  be  separated  into  a  portion  con- 
taining the  nuclear  material  and  a  portion  containing  no  nuclear 
material. 

Those  portions  containing  no  nuclear  material  will  live  for  a 
while,  even  ingest  food  and  move  around  in  the  case  of  the  ameba 
for  a  period  as  long  as  14  days.     (Fig.  10.)     Eventually,  however, 

32 


STEUCTUEAL  AND  CHEMICAL  UNITS  OF  THE  BODY 


all  the  nucleusless  fragments. die.  On  the  other  hand  fragments 
of  cells  containing  pieces  of  the  nucleus  are  capable  of  continued 
life  and  complete  regeneration  and  reproduction.  Even  such  com- 
plicated forms  of  unicellular  life  as  a  stentor  will  regenerate  from 


Fig.  14. — Special  forms  of  nuclei.     (Wilson.) 

A.  Permanent  spireme-nucleus,  salivary  gland  of  Chironomus  larva.  Chro- 
matin in  a  single  thread,  composed  of  chromatin-discs  fchi'omomeres),  ter- 
minating at  each  end  in  a  true  nucleolus  or  plasmosome.  B.  Permanent 
spireme-nuclei,  intestinal  epithelium  of  dipterous  larva  Ptychopters.  (Van 
Gehuchten).  C.  The  same,  side  view.  D.  Polymorphic  ring-nucleus,  giant- 
cell  of  bone-marrow  of  the  rabbit;  c.  a  group  of  centrosomes  or  centrioles. 
E.  Branching  nucleus,  spinning  gland  or  butterfly-larva  (Pieris) . 

nucleated  pieces  all  the  organs  of  its  cell.    These  include  its  mouth, 
cilia,  stalk,  and  various  vacuoles.     (Figs.  11,  12  and  13.) 

3.  In  rapidly  growing  organs  such  as  the  growing  tips  of  plants 
nuclear  changes  are  very  prominent  and  the  nuclei  are  situated 
nearest  the  point  of  greatest  growth. 

34 


STEUCTUEAL -AND  CHEMICAL  UNITS  OF  THE  BODY 

4.  In  actively  functionating  organs  such  as  tlie  salivary  glands 
of  lepidopterous  larvse  the  nucleus  becomes  much  branched  and 
enlarged.     (Fig.  14.) 

5.  During  the  period  of  growth  of  eggs,  and  this  is  especially 
noticeable  in  the  germinal  cells  of  a  shark,  the  nuclear  chromosomes 
become   very   large   and   elongated.     They   are   then   less   deeply 


Fig.  15. — Chromosomes  of  the  germinal  vesicle  in  the  shark  Pristiurus,  at  different 
periods,  drawn  to  the  same  scale.     (Wilson.) 

A.  At  the  period  of  maximal  size  and  minimal  staining-capacity  (egg  3  mm. 
in  diameter).  B.  Later  period  (egg  13  mm.  in  diameter).  C.  At  the  close  of 
ovarian  life,  of  minimal  size  and  maximal  staining-power. 

stained.  Finally  immediately  before  fertilization  they  become 
smaller  in  size  but  stain  intensely.  (See  Fig.  15.)  We  may  say 
that  the  cytoplasm  represents  the  seat  of  the  functional  phenomena 
of  the  cell,  the  seat  of  its  activities,  but  that  the  nucleus  represents 
the  seat  of  those  forces  which  renew  the  apparatus  of  functional 
activity,  the  organ  controlling  the  vital  and  synthetic  processes  of 
the  cell,  the  organ  responsible  for  the  transmission  of  the  hereditary 
characters  of  the  cell. 

36 


The  material  basis  of  the  body 

Elements  Composing  the  Body — The  following  twelve  elements 
enter  into  the  composition  of  every  living  being :  carbon,  hydrogen, 
oxygen,  nitrogen,  sulphur,  phosphorus,  chlorine,  potassium,  sodium, 
calcium,  magnesium  and  iron. 

In  addition  to  these  any  of  seven  other  elements  may  be  found 
in  certain  forms  of  life.  They  are  silicon,  iodine,  fluorine,  bromine, 
aluminium,  manganese  and  copper. 

Law  of  the  Minimum— The  growth  of  any  living  being  is 
limited  by  that  constituent  of  its  food  which  is  available  to  it  in 
the  smallest  quantities.  In  the  case  of  plants  which  cannot  move 
around  this  concerns  that  element  of  its  structure  which  is  present 
in  the  smallest  quantity  in  its  immediate  neighborhood.  This  fact 
is  formulated  into  a  law  known  as  the  "Law  of  the  Minimum." 

The  elements  of  the  earth's  crust  which  are  present  in  the 
smallest  amount  in  most  soils  are  potassium,  nitrogen  and  phos- 
phorus. These  elements,  therefore,  determine  the  growth  of  most 
crops. 

The  Prominence  of  Carbon  in  the  Living  Body — Carbon  forms 
by  far  the  greater  part  by  weight  of  the  elementary  constituents 
of  all  protoplasm.  All  the  compounds  of  living  bodies  are  com- 
pounds of  carbon.  It  is  for  this  reason  that  the  term  organic 
chemistry  is  applied  to  the  compounds  of  carbon. 

The  carbon  in  them  is  not  present  in  the  completely  oxidized 
form.  In  other  words,  all  its  compounds  in  the  living  cell  are 
combustible. 

The  Form  and  Distribution  of  Carbon  in  the  Inorganic  World 
— In  the  earth,  apart  from  living  beings,  all  carbon  does  exist  in 
a  completely  oxidized  form.  Vast  quantities  of  carbon  are  stored 
up  in  the  earth's  crust  in  the  form  of  carbonates  of  the  alkali 
earths  as  chalk  and  limestone.  These  forms  of  carbon  are  insoluble 
and  unavailable  to  the  plant  life. 

The  Source  of  Carbon  to  the  Living  Things — Living  beings 
derive  all  their  carbon  from  the  small  quantity  of  carbon  dioxide 

38 


THE   MATEEIAL   BASIS   OF   THE   BODY 

in  the  atmosphere.  Carbon  dioxide  exists  in  the  atmosphere  in 
the  proportion  of  four  parts  in  every  10,000.  By  plant  life  this  is 
converted  into  the  incompletely  oxidized  form  of  carbon,  the 
carbohydrates.     The  following  formula  represents  the  reaction: 

6CO2  +'  5H2O  =z  CeH^oOg  +  60, 

The  machine  for  this  conversion  is  the  chlorophyl  granules 
of  the  plant  and  the  energy  comes  from  the  energy  in  the  sun's 
rays.  <=— "^^ 

The  energy  of  the  sun's  rays  becomes  converted  or  stored 
up  as  potential  energy  in  the  carbohydrates  of  the  plant.  Each 
gram  of  starch  is  capable  of  yielding  4,500  calories  of  heat  energy. 

The  deoxidation  of  the  carbon  can  be  carried  a  step  further 
within  plants.  The  carbohydrates  may  be  converted  into  fats  as 
represented  by  the  following  formula : 

SCgHigOg  —  8O2  =  CigHgeOg 

(sugar)  {stearic  acid) 

The  energy  for  this  reaction  is  obtained  by  an  oxidation  of 
other  carbohydrates  in  the  plant. 

The  potential  energy  contained  in  the  fats  is  even  greater — 
one  gram  of  fat  yielding  on  oxidation  9,000  calories  of  heat  energy. 
Animal  life  cannot  utilize  the  carbon  of  the  atmosphere.  They 
obtain  their  carbon  entirely  in  the  form  of  prepared  carbohydrates 
and  fats  which  the  plants  have  manufactured. 

The  Form  in  Which  Carbon  Leaves  the  Plants  and  Animals — 
Carbon  leaves  both  the  plant  and  animal  in  the  completely  oxidized 
form  of  carbon  dioxide.  "While  the  plants  give  up  oxygen  to  the 
atmosphere  and  take  from.it  carbon  dioxide  and  the  animals  are 
constantly  breathing  out  carbon  dioxide  and  taking  in  oxygen,  it 
must  not  be  thought  that  plants  in  the  processes  of  their  own 
life  do  not  also  break  down  their  own  complex  organic  compounds 
with  the  formation  of  carbon  dioxide  and  consumption  of  oxygen. 

The  process  of  dissimilation  as  well  as  assimilation  is  going 
on  within  plants  as  well  as  within  animals;  dissimilation  and 
assimilation  are  common  to  both. 

The  Effect  of  Vital  and  Cosmic  Influences  on  the  Supply  of 
Carbon  Dioxide — All  forms  of  life,  therefore,  tend  to  maintain 

40 


THE   MATEEIAL   BASIS   OF   THE   BODY 

an  even  balance  between  the  amount  of  carbon  dioxide  and  oxygen 
in  the  atmosphere. 

There  are,  however,  other  causes  at  work  which  are  const'antlj 
tending  to  rob  the  atmosphere  of  carbon  dioxide.  Probably,  there- 
fore, the  amount  of  carbon  dioxide  is  becoming  less  and  less  as  the 
world  grows  older.  At  an  early  period  in  this  earth's  history 
constant  volcanic  action  was  discharging  carbon  dioxide  into  the  " 
atmosphere.  At  the  high  temperature  which  then  existed  on  the 
earth,  silica  had  a  stronger  affinity  for  the  bases  than  carbon 
dioxide.  In  the  presence  of  silica,  therefore,  carbon  dioxide  would 
be  liberated  from  chalk  with  the  formation  of  calcium  silicate.- 
At  the  temperatures  now  present  on  the  earth  carbon  dioxide  is 
a  stronger  acid  than  silica  and  unites  with  the  calcium  forming, 
calcium  carbonate  and  setting  free  the  silica.  Calcium  carbonate 
(chalk  or  lime  stone)  is  insoluble  and  hence  unavailable  to  plant 
or  animal  life.  ■*. 

Myriads  of  sea  animals  are  constantly  locking  up  carbon  in 
an  insoluble  form  as  coral  deposits  which  are  formed  of  calcium  , 
carbonate. 

The  Source  of  Hydrogen  to  Plant  and  Animal  Life — Hydrogen 
is  taken  into  both  plant  and  animal  life  in  the  form  of  water;  a 
small  negligible  quantity  enters  as  ammonia. 

Oxygen — Is  the  only  element  taken  in  by  all  life  in  the  free 
state.  It  forms  one-fifth  of  the  atmosphere,  the  other  four-fifths 
being  formed  by  nitrogen.  Oxygen  serves  two  purposes  within 
the  body.  It  forms  a  part  of  the  chemical  substances  of  which 
the  body  is  composed,  in  this  respect  resembling  the  other  elements. 
It  also  is  that  agent  which  alone  makes  possible  the  utilization 
by  the  body  of  its  stored  up  potential  energy.  This  is  accom- 
plished by  the  oxidation  of  its  carbon  containing  compounds  into 
carbon  dioxide  and  water.  This  process  conducted  within  the  cells 
may  be  spoken  of  as  internal  respiration. 

Nitrogen — Is  only  indirectly  obtained  from  the  atmosphere. 
It  possesses  very  feeble  combining  powers  and,  therefore,  most  of 
the  nitrogen  of  the  world  exists  in  a  free  statjgX  As  mentioned, 
it  constitutes  four-fifths  of  the  atmosphere.  \iijQN;his  form,  how- 
ever, it  is  unavailable  to  both  plants  and  animals.  AniAials  are 
only  able  to  assimilate  nitrogen  in  the  form  of  complex  bodies  called 
proteins  formed  for  them  by  plants.     Even  plants  themselves  can 

42 


THE   MATEEIAL   BASIS   OF   THE   BODY 

only  assimilate  nitrogen  in  the  form  of  ammonia  or  nitrates.  Some 
of  the  molds  can  utilize  ammonia;  other  molds  and  many  of  the 
higher  plants,  especially  all  the  food  producing  cereals,  can  only 
assimilate  nitrogen  in  the  form  of  nitrates. 

The  Source  of  the  Nitrates — It  is  a  matter  of  interest,  there- 
fore, to  know  the  various  sources  from  which  the  nitrates  are 
replaced. 

1.  Every  thunder  storm  accompanied  with  the  passage  of 
electricity  through  the  air,  even  when  the  discharges  are  silent, 
is  accompanied  with  the  formation  of  ammonium  nitrite  which  is 
carried  to  the  earth  in  the  rain. 

N2  +  2H,0  =  NH.NOo 

2.  A  number  of  bacteria  exist  which  are  efficient  agents  in, 
not  only  the  extraction  of  nitrogen  from  the  air,  but  also  in  the 
transformation  of  nitrogen,  combined  in  forms  unsuited  to  plant 
life,  as  the  nitrites,  into  forms  suited  for  assimilation  by  plants, 
the  nitrates.  No  one  form  accomplishes  any  more  than  one  of 
these  changes. 

a  The  bacterium  nitrosomonas  is  able  to  transform  ammonia 
into  ammonium  nitrite. 

&  The  bacterium  nitromonas  is  capable  of  transforming  ni- 
trites into  nitrates.  Inasmuch  as  the  end  product  of  the  nitrogen 
compounds  in  decaying  organic  matter  is  ammonia,  these  two 
bacteria  may  be  utilized  to  scientifically  dispose  of  sewage  in 
such  a  manner  that  its  nitrogenous  compounds  may  be  made 
available  for  plant  life. 

c  The  bacterium  Clostridium  is  capable  of  fixing  as  nitrites 
the  free  nitrogen  of  the  air  contained  within  the  soil.  These 
organisms  are  anaerobic  but  are  capable  of  growing  in  the  soil 
because  of  the  presence  of  other  aerobic  bacteria  which  protect 
them  from  the  oxygen. 

d  Nodules  rich  in  nitrogen  will  form  upon  the  roots  of  certain 
leguminous  plants  grown  in  soils  inoculated  by  certain  bacteria 
described  by  Beyernick. 

These  nodules  when  examined  are  found  to  be  swarming  with 
bacteria,  and  the  soil  in  which  such  a  crop  is  grown  is  richer  in 
nitrogen  after  the  growth  of  such  a  crop  than  before.  These  bac- 
teria are  able,  therefore,  to  fix  the  nitrogen  of  the  air  in  forms 

44 


THE  MATERIAL  BASIS  OF  THE  BODY 

available  to  plant  life  within  the  soil.  They,  however,  can  only 
effect  this  change  by  growth  in  symbiosis  with  leguminous  plants. 

Sulphur — Is  assimilated  by  plants  in  the  form  of  sulphates 
in  which  form  it  exists  in  all  soils.  "Within  the  plants  it  becomes 
deoxidized  at  the  expense  of  the  energy  of  the  carbohydrates  and 
then  built  up  into  the  complex  protein  molecule.  The  body, 
cystine,  is  a  sulphur-containing  group  of  the  protein  molecule.  All 
the  sulphur  which  becomes  a  part  of  the  animal's  protoplasm  is 
taken  in  by  the  animal  in  protein  form. 

The  animal  cannot  form  its  own  proteins  from  the  sulphur 
salts.  Sulphur  leaves  the  animal  body  fully  oxidized  as  sulphates. 
The  amount  of  these  salts  leaving  the  body  is,  therefore,  like  the 
amount  of  nitrogen  leaving  the  body  a  true  index  to  the  amount 
of  protein  metabolism  going  on  within  the  body. 

The  Source  of  the  Phosphorus  to  the  Plant  and  Animal  Body 
— Phosphorus  is  assimilated  by  plants  in  the  form  of  phosphates 
in  the  soil.  It  also  is  built  up  by  plants  into  complex  organic 
substances  belonging  to  the  class  of  proteins,  but  in  addition  to 
entering  into  the  formation  of  proteins  it  also  enters  into  the 
formation  of  certain  complex  fats  in  the  body.  Moreover  it  is  not 
a  part  of  all  proteins.  It  appears  to  be  an  essential  part  of  proteins 
forming  the  nucleus  of  the  cells. 

By  animals  practically  all  phosphorus  is  assimilated  in  the 
forms  of  the  complex  protein  called  nuclein  and  the  complex  fat 
called  lecithin. 

The  Function  and  Source  of  the  Iron  to  the  Plant  and  Animal 
— No  element  is  more  important  to  the  body.  Even  though  pres- 
ent in  very  small  proportion,  only  6  grams  to  the  whole  body,  it  is 
absolutely  essential.  The  oxygen  carrying  functions  of  the  body 
cannot  be  conducted  without  it.  This  function  in  animals  is  per- 
formed by  hemoglobin  and  by  the  iron  containing  portion  of  the 
hemoglobin  molecule. 

In  plants  iron  forms  an  essential  constituent  of  the  chlorophy] 
molecule,  that  substance  which  accomplishes  the  deoxidation  of 
carbon  for  the  plants. 

Probably  minute  traces  of  iron  in  the  composition  of  the  proto- 
plasm of  all  cells  assist  in  the  intracellular  oxidative  processes. 


46 


I 


THE  CHEMICAL  UNITS  OF  THE  BODY 

The  Foodstuffs  of  the  Body — The  twelve  elements  composing 
the  tissues  of  the  animal  body  can  only  be  united  together  into 
the  numerous  complex  substances  forming  the  tissues  of  the  body 
by  a  series  of  intricate  chemical  processes  carried  on  within  the 
cells  of  the  body.  These  cells  may  be  regarded  as  so  many  chemical 
laboratories  within  which  are  elaborated  the  changes  resulting  in 
the  production  of,  first,  the  substances  constituting  the  cells  them- 
selves, second,  the  substances  necessary  for  the  liberation  of  energy 
and  third  the  substances  representing  the  specific  activities  of 
cells. 

In  only  certain  of  the  plant  cells  can  these  changes  begin 
with  either  the  individual  elements  or  their  simplest  compounds. 
In  the  animal  body  these  changes,  with  the  exception  of  inorganic 
salts  and  water,  begin  only  with  three  kinds  of  complex  food- 
stuffs. For  the  animal  onlj^  these  three  kinds  of  foodstuffs  are 
capable  of  being  broken  apart  during  the  process  of  digestion 
into  certain  definite  simpler  bodies  from  which  alone  the  animal 
can  construct  first  its  own  tissues  and  second  its  energy-yielding 
compounds,  and  third,  the  products  of  specific  cellular  activity. 

These  simpler  basic  compounds  are  a  definite  number  of  chem- 
ical substances  which  may  be  termed  the  chemical  units  of  the 
body  because  the  body  can  with  these  and  only  these  begin  the 
complicated  series  of  changes  essential  for  its  life.  The  three 
foodstuffs  which  are  capable  of  yielding  the  chemical  units  of 
the  body  are  substances  called  carbohydrates,  fats  and  proteins. 
Each  of  these  will  be  defined  and  described  later. 

The  Fundamental  Elements  of  Life — The  carbohydrates,  fats 
and  proteins  are  all  compounds  of  carbon.  In  fact  carbon  may  be 
termed  the  fundamental  element  of  the  body.  It  is  entirely  due 
to  the  peculiar  combining  properties  of  carbon  that  the  infinite 
variety  of  organic  compounds  incidental  to  cell  life  are  possible. 

48 


THE   CHEMICAL  UNITS   OF  THE  BODY 

The  Fundamental  or  Mother  Substances  of  the  Compounds 

of  Carbon — All  organic  compounds  of  carbon  may  be  regarded 

as  modifications  of  two  fundamental  substances.     Each  of  these 

two  substances  are  composed  of  carbon  and  hydrogen,  which  are 

united  together  in  the  following  manner  in  the  two  fundamental 

substances : 

H  H 

I  I 

H— C— H  C 

I  ■  /  \ 

H  'J  H— C         C— H 

il  I 

H— C         C— H 

\   / 
C     p 

H         G.      '^ 

The  Manner  in  Which  These  Simple  Compounds  May  Be 
Altered  to  Form  a  Great  Variety  of  Different  Compounds — The 

first  compound,  CH^,  is  known  as  methane,  or  marsh  gas,  and  by 
replacing  one  or  more  of  its  hydrogen  atoms  with  other  atoms  or 
combinations  of  atoms,  together  forming  a  group,  and  capable 
as  a  unit  of  taking  the  place  of  one  or  more  of  the  hydrogen 
atoms  of  methane,  a  whole  series  of  other  organic  compounds 
.may  be  formed. 

The  Mother  Substances  of  These  Variations — One  of  the 
groups  which  may  replace  one  of  the  hydrogen  atoms  of  methane 
may  be  methane  itself.  We  then  have  two  methane  molecules 
combined  together  thus: 

H'     H 

I         I 
H  — C  — C  — H 

I.       I 
H      H 

This  compound  is  called  ethane,  and  is  the  next  higher  member 
of  the  methane  group.  Still  higher  members  are  made  in  a 
similar  manner  by  successively  attaching  additional  methane 
groups.  Thus  propane  is  a  combination  of  three  methane  groups, 
and  has  the  formula: 

50 


C- 


THE   CHEMICAL   UNITS   OF   THE   BODY 

H      H     H 

I        I        I 
H— C— C— C— H 

III 
H     H     H 

Its  abbreviated  formula  is  CH3CH2CH3. 

Butane  is  CHeTCHJ^CHg. 

Pentane  is  CH3(CH2)3CH3. 

Hexane  is  CH3(CH-.),CH3. 

Heptane  is  CH3(CH2)5CH3. 

Octane  is  CH3(CH2)6CH3,  etc. 

These  substances  together  with  still  higher  members  of  the 
series  are  termed  the  mother  substances  of  the  methane  series. 

The  More  Important  Compounds  of  the  Mother  Substances — 
The  more  important  compounds  of  the  methane  series,  are  the 
alcohols,  the  aldehydes  and  the  acids. 

Alcohols — An  alcohol  is  formed  by  the  introduction  of  an 
OH  group,  called  the  hydroxyl  group.  Thus  if  one  of  the  hydrogen 
atoms  of  methane  or  ethane  or  propane,  is  replaced  by  a  hydroxyl 
group  we  have  methyl,  or  ethyl,  or  propyl  alcohol.  Their  formulas 
are: 
H 

I 
H  — C  — OH  or  CH3— OH,  and  CH3CH2OH  and  CH3,(CH2)20H 

I 
H 

The  still  higher  alcohols  are: 
Butyl  alcohol,  CHgCCHJsOH. 
Pentyl  alcohol,  CH3(CH2)40H. 
Hexyl  alcohol,  CH3(CH2)50H. 
Heptyl  alcohol,  CK.iCR,) .OK. 
Octyl  alcohol,  CR,(CH),),OH. 
Nonyl  alcohol,  CH3(CH2)80H. 
Cetyl  alcohol,   CH3(CH2)90H. 
Ceryl  alcohol,   CH3(CH,)ioOH. 
Myricyl  alcohol,   CH3(CH,),,0H,  etc. 

Aldehydes — An  aldehyde  is  formed  by  replacing  two  of  the 

52 


THE   CHEMICAL  UNITS   OP  THE  BODY 

hydrogen  atoms  with  one  atom  of  oxygen.     Methyl,   ethyl  and 
propyl  aldehyde  have  this  formula : 

H  —  C  —  H,  or  CH2O,  and  CH3CHO  and  CHgCH^CHO 

II 
O 

The  aldehydes  are  characterized  by  strong  combining  powers. 
In  virtue  of  this  they: 

1.  Act  as  reducing  agents  to  certain  compounds  containing 
oxygen  being  themselves  oxidized  into  acids  thus: 

CH3 

I 
CHO  +  0  r=  CH3 

I 
COOH 

2.  On  warming  with  phenyl  hydrazin  they  give  the  typical 
compounds  known  as  hydrazones  and  osozones. 

3.  They  readily  form  addition  products  with  ammonia  and 
other  substances  as  sodium  sulphite,  thus:  \         , 

CH3  CH3  -KJ-TT 

I        +NH3=|/^^2  -    , 

CHO  C— H  i 

^OH 

CH3  CH3 

I      +NaHS03=  I     /OH 
CHO  CH( 

\SO3Na 

4.  They  all  possess  a  strong  tendency  to  combine  with  them- 
selves and  thus  multiply  their  structure  by  polymerization,  thus: 

3(CA0)=CeH,A 

Acids — An  organic  acid  of  the  methane  series  is  made  by 
replacing  three  of  the  hydrogen  atoms  attached  to  one  carbon  atom 
of  the  mother  substance.     One  of  these  atoms  is  replaced  by  a 

54 


THE   CHEMICAL   UNITS   OF   THE   BODY 

hydroxyl  group,  and  two  others  by  one  atom  of  oxygen.  Thus 
formic  acid  is  the  organic  acid  of  methane,  and  acetic  acid  is  the 
organic  acid  of  ethane,  and  propionic  acid  is  the  organic  acid  of 
propane.    The  formulas  of  these  acids  are: 


Formic  acid: 


H 


C  — 0  — H 


-a 


or  HCOOH 


H 


Acetic  acid : 


H  — C  — H 


or  CH,COOH 


0^  C  —  0  —  H 
H 


Propionic  acid:H  —  C  —  H 

I 
H  — C  — H 


or  CH3CH2COOH 


0=0— 0—H 


Butyric  acid, 

Valeric  acid, 

Caproic  or  hexoic  acid, 

Enanthylic  or  heptoic  acid, 

Caprylic  or  octoic  acid, 

Pelayonic  or  nonoic  acid, 

Capric  acid, 

Laurie  acid 

Myristic  acid,     - 

Palmitic  acid, 

Margaric  acid, 

Stearic  acid. 


CH3(CH2)2C00H. 

CHgCCHJgCOOH. 

CH3(CH04COOH. 

CH3(CHJ5C00H. 

CH3(€H2)6COOH. 

CH3(CH2),C00H. 

CH3(CH2)3COOH. 

CH3(CH2)ioCOOH. 

CK,{ClIo)  ,,COOK. 

CHgCCHJi.COOH. 

CH3(CH2)i5C00H. 

CH3(CH2)ieCOOH,  etc. 


The  modified  carbon  atom,  with  its  attached  oxygen  and 
hydroxyl  atoms,  is  called  the  carboxyl  group.  By  replacing  the 
hydrogen  atom  belonging  to  the  other  carbon  atoms  of  the  mole- 
cule of  an  organic  acid  we  can  obtain  an  oxyacid  or  a  keto-acid 
or  an  amino-acid. 

56 


THE   CHEMICAL   UNITS   OF   THE   BODY 

The  oxyacid  is  obtained  by  introducing,  as  described,  a  hydroxyl 
group.     Thus  oxy propionic  acid  is 

CH2OH 

I 
H— C— H  ^ 

I 
0  =  C  — O  — H         ■         1^ 

A  keto-acid  is  formed  by  the  introduction  in  the  same  manner 
of  an  atom  of  oxygen,  thus: 


H  — C  =  0 


H-C-H^/  \\^Y-'^% 


0=C— 0— H 

An  amino-acid  is  formed  by  the  introduction  of  the  ammonia 
group  in  place  of  one  of  the  hydrogen  atoms  belonging  to  some 
other  carbon  atom  of  an  organic  acid  than  the  one  forming  the 
carboxyl  group. 

Thus  amino-aeetie-acid  is 

H2—  C  —  NH2 

I 

Or=C  — 0  — H 

By  replacing  the  hydroxyl  group  of  an  organic  acid  with  am- 

CH3 
monia  an  acid  amide  is  formed;  thus  from  acetic  acid    | 

CH3  COOH 

acetamide     |  may  be  formed. 

CONH2 
Amines  may  be  regarded  as  formed  by  replacing  one  or  more 
of  the  hydrogen  atoms   of  the  ammonia  itself  with  an  organic 
radical,  thus: 

( Methylmnin  e )      ( Dimetliylamine )      ( Trimethylamine ) 

/CH3  /CH3  yCHs 

N— H  N— CH3  N— CH3 

58 


THE   CHEMICAL  UNITS   OF  THE   BODY 

Unsatisfied  Series  of  Carbon  Compounds — The  mother  sub- 
stances of  the  methane  series  or  their  modified  compounds  may 
be  further  varied  in  consequence  of  a  union  of  a  various  number 
of  the  carbon  atoms  by  more  than  one  bond.  Examples  of  these 
compounds  are : 

Ethylene  or  ethene,  HgC  =  CHo,  or  C2H4. 

Acetylene,  HC  =  CH,  or  C2H2. 

Propylene  or  propene,  CgHg. 

Butylene  or  butene,  C^Hg. 

Amylene  or  pentene,  CgH^o. 
.    Hexylene  or  hexene,  CgHia,  etc. 

''  The  Modifications  of  the  Benzene  Series — The  second  mother 
substance  of  the  organic  compounds  is  benzene.  From  it  may 
be  formed  all  the  modifications  of  the  methane  series  by  replacing 
appropriate  hydrogen  atoms. 

H  H 

I  I 

C  C 

H— C        C— H      H— a  1/C— H 
Thus  benzene  is  CgHg  or  [|  |  or  |    //   \ 

H— C        C— H      H— C/ r^C— H 
\/  \l/ 

c  c 

H  H 

Naphthalene  is  two  benzene  molecules  united  together  thus: 

H  H 

C  C 

y  \  /  \ 

HC  C  CH 

I  II  i 

HC  C  CH 

\   /   \   / 

c       c 

H  H 

Carbolic  acid  or  phenol  may  be  considered  the  alcohol  of  ben- 
zene. It  is  CgHgOH.  Benzoic  acid  may  be  considered  the  simplest 
acid  formed  from  benzene.    It  is  CgHgCOOH. 

By    a    combination    various    number    of    methyl    groups    or 

60 


THE   CHEMICAL   UNITS   OF   THE   BODY 

methane  radicals  with  benzene  a  whole  series  of  organic  com- 
pounds of  increasing  complexity  and  analogous  to  the  methane 
series  may  be  formed  thus : 

Benzene  is  CgHg. 

Toluene  is  CeH.CHe. 

Xylene  is  CeH,(CH3)3. 

Mesitylene  is  C6H3(CH3)3. 

^^^^'^^^'^^^<CH;.CH,CH3,  etc. 

According  as  the  inserted  methyl  groups  are  attached  to  the 
two  top  carbon  atoms  of  the  benzene  ring,  or  the  top  and  next 
to  the  bottom  carbon  atom,  or  opposite  carbon  atoms,  the  com- 
pound is  called  ortho,  meta  or  para  xylene. 

It  must  not  be  considered  that  the  above  illustrations  con- 
stitute the  only  possible  modifications  of  the  mother  substances  of 
the  organic  compounds.  Very  many  other  chemical  elements  may 
be  combined  in  various  ways  with  them  as  well  as  numerous  other 
modifications  of  the  kind  illustrated  above.  The  above  substances 
are  only  illustrations  of  some  of  the  more  important  types  of 
compounds.  They  demonstrate  the  enormous  number  of  varia- 
tions in  the  combining  power  of  carbon :  a  property,  in  fact,  upon 
which  depends  the  elaboration  of  substances  capable  of  perform- 
ing the  living  activities  of  cells. 

The  Vital  Synthesis  of  the  Carbohydrates — ^As  has  been  ex- 
plained, the  original  source  of  the  carbon  for  the  formation  of  all 
organic  compounds  found  in  living  cells  is  the  small  percentage 
(.03%)  of  carbon  dioxide  of  the  air.  It  is  picked  out  of  the  atmos- 
phere by  the  chlorophyl  granules  or  chloroplasts  of  the  plants. 
These  granules  are  responsible  for  the  green  of  the  leaves  of  plants. 
The  leaf  of  a  plant  is  so  formed  that  it  presents  a  maximum 
absorbing  surface  and  at  the  same  time  a  structure  limiting  the 
loss  of  water  by  evaporation.  One  square  meter  of  certain  leaves, 
the  absorbing  power  of  which  has  been  measured,  can  consume 
784  c.c.  of  carbon  dioxide  per  hour  and  from  this  form  one  gram 
of  solid  material. 

It  is  possible  for  the  chloroplasts  to  work  even  more  rapidly 
than  this,  because  there  is  only  .03  per  cent,  of  carbon  dioxide  in 
the  atmosphere,  and  in  an  atmosphere  containing  1  per  cent,  of  car- 
bon dioxide  a  leaf  can  take  up  137  per  cent,  more  carbon.    Increas- 

62 


THE   CHEMICAL  UNITS   OF  THE  BODY 

ing  the  amount  of  carbon  dioxide  over  1  per  cent,  produces  no 
greater  increase  in  the  absorbing  power  of  the  leaf. 

The  first  change  produced  in  the  absorbed  carbon  .dioxide  is  the 
tearing  away  of  one  atom  of  oxygen  and  its  replacement  by  two 
atoms  of  hydrogen,  according  to  the  following  formula : 

H 
CO2  +  3H2O  =  2H2O2  +  C  =  0  / 

H 

The  first  step,  therefore,  is  the  formation  of  hydrogen  peroxide 
and  formaldehyde. 

The  hydrogen  peroxide  which  is  formed  with  it  is  a  strong  oxi- 
dizing agent  and  would  quickly  oxidize  the  formaldehyde  unless  the 
removal  of  the  hydrogen  peroxide  was  provided  for.  There  occurs, 
however,  in  plants  a  ferment  called  catalase.  It  is  probably 
this  which  accomplishes  the  removal  of  the  hydrogen  peroxide  by 
breaking  it  up  into  water  and  free  oxygen.  It  is  thus  that  the 
plants  give  off  oxygen  to  the  air.  The  retained  formaldehyde 
now  undergoes  further  changes.  A  characteristic  of  all  aldehydes 
is  the  ease  with  which  they  undergo  polymerization.  This  process 
simply  means  a  doubling  of  the  formula  until  a  six-carbon  atom 
compound  is  formed  which  has  the  same  relative  number  of  atoms 
in  the  molecule  as  formaldehyde  possesses.  The  resulting  body 
is  still  an  aldehyde  and  because  it  contains  six-carbon  atoms  is 
called  a  hexose,  or  one  of  the  sugars.  The  polymerization  of 
formaldehyde  into  a  hexose  or  a  sugar  may  be  represented  thus: 
6CH3O  =  CeHi^Oe. 

The  Four  Hexoses — The  structural  formulas  of  four  of  the 
hexoses  capable  of  assimilation  by  the  body  are  shown  on  page  66. 

It  will  be  appreciated  that  the  formulas  of  these  four  sugars 
differ  from  one  another  according  to  the  relation  of  the  H  atoms 
and  the  OH  group  of  the  middle  four  carbon  atoms.  This  dif- 
ference makes  the  molecule  asymmetrical  on  its  two  sides  and-  is 
responsible  for  the  property  which  these  sugars  possess  of'  rotat- 
ing polarized  light  in  varying  degrees  to  the  right  or  left.  Inas- 
much as  there  are  four  asymmetrical  carbon  atoms  in  this  com- 
pound, it  is  possible  to  have  sixteen  different  sugars,  all  having 

64 


THE   CHEMICAL   UNITS   OF   THE   BODY 


{d — mannose) 

H 

1 

(d — glucose) 

H 

1 

1 
C  =  0 

1 

1 
C  =  0 

1 

H- 

1 
-0  — C  — H 

1 

I 
H— C— 0— H 

1 

H- 

1 
-0  — C  — H 

1 

H- 

1 
-0— C— H 

1 
H  — C  — 0  — H 

H— C— 0— H 

H— C— 0— H 

1 

H— C— 0— H 

1 

1 
H— C— 0— H 

1 

1 
H— C— 0— H 

1 

1 
H 

1 
H 

{d — fructose) 
H 

(d — galactose) 

H 

1 

H  — C  — 0  — H 

1 

1 
C  =  0 

1 

1 

c  =  o 

1 

1 
H  — C  — 0  — H 

H- 

1 
-0  — C  — H 

1 

H- 

-0  — C  — H 

1 

1 
H  — C  — 0  — H 

1 

H- 

1 
-0  — C  — H 

1 

1 
H  — C  — 0  — H 

1 
H  — C  — 0  — H 

1 

H— C— 0— H 

1 

1 
H— C— 0— H 
1 

1 
H 

1 
H 

the  formula  CgHisOe.  Of  these  sixteen  sugars  only  the  four  men- 
tioned are  of  any  physiological  importance  because  only  these  can 
be  utilized  by  the  body. 

The  Disaccharides  and  the  Formation  of  Starch  from  the 
Hexoses — By  means  of  other  granules  in  the  plant  cells  called  the 

66 


THE   CHEMICAL  UNITS   OF  THE  BODY 

leucoblasts  the  simple  hexoses  are  combined  together,  with  the 
loss  of  water,  in  a  manner  to  constitute  the  complex  starch  mole- 
cule. 

In  the  formation  of  starch  from  sugar  unquestionably  some 
of  the  disaccharides  represent  stages  in  the  process.  From  a  physi- 
ological standpoint  three  of  these  bodies  are  of  particular  impor- 
tance. These  are  maltose,  lactose,  and  cane  sugar.  Maltose  is  a 
combination  of  two  molecules  of  glucose.  For  the  sake  of  illus- 
tration its  structural  formula  is  given : 

H 

I 
0 C  — H 

H  — C  


H— C— 0— H 
H— 0— C— H 

H  — C  — 


H— 0— C— H 

I    . 
H— 0— C— H 

H— C— 0— H 


H— C— 0— H  H— 0— C— H 

I  I 

H  — C  — 0  — H  C  — H 

I  li 

H  0 

The  formulas  for  lactose  and  cane  sugar  are  precisely  similar. 

Lactose  is  simply  a  combination  of  one  molecule  of  galactose 
and  glucose,  while  cane  sugar  is  a  combination  of  fructose  and 
glucose.  yr^^b^'O  ^g-j^ 

Starch  possesses  the  formula  CgHioOs,  that  is,  the  number  of 
carbon,  hydrogen,  and  oxygen  atoms  bear  this  relation  to  each 
other,  but  the  whole  molecule  is  composed  of  constituent  groups 
combined  together  so  that  altogether  the  starch  molecule  is  a  very 
large  one  with  atomic  weight  of  not  less  than  32400.  Its  empirical 
formula  may  be  represented  by  100  ^x^i^f^w,  or  (80  Q-^^^^O^^.- 
40  CeliioOs).  Probably  the  80  C12H20O10  portion  consists  of  ten 
groups  of  four  double  molecules  of  maltose  united  together,  with 
the  loss  of  one  molecule  of  water,  around  the  40  CgHioOs  portion. 

68 


THE   CHEMICAL   UNITS   OF   THE   BODY 

Each  double  molecule  of  maltose  may  be  considered  a  dextrin 
body,  perhaps  no  other  than  ethro-dextrin.  The  central  portion 
of  the  molecule,  the  40  CgH^oOg,  is  very  resistant  to  further  change. 
It  may  be  no  less  than  achrodextrin,  and  probably  consists  of  40 
glucose  molecules  united  together,  with  the  loss  of  thirty-nine 
molecules  of  water. 

The  Relation  of  Processes  of  BeducHon  of  the  GO 2  to  the  Storage 
of  Potential  Energy — It  will  be  appreciated  that  the  process  of 
formation  of  sugar  or  starch  from  carbon  dioxide  is  a  process  of 
deoxidation  or  reduction  of  the  carbon  of  the  atmosphere.  CO2  is 
a  completely  oxidized  form  of  carbon  while  sugar  and  starch  are 
only  incompletely  oxidized  forms.  The  reverse  of  deoxidation,  of 
reduction,  is  oxidation.  It  is  illustrated  by  the  burning  piece 
of  wood  which,  by  the  heat  applied  from  the  flame  which  lighted 
the  wood,  transformed  its  incompletely  oxidized  carbon  and 
Hj  into  a  gaseous  state  in  which  state  it  unites  with  the  oxygen 
of  the  atmosphere  to  form  a  completely  oxidized  form  of  carbon 
or  CO2.  This  process  of  oxidation,  as  all  oxidative  processes,  gives 
off  heat  and  sufficient  heat  to  cause  the  continued  liberation  of 
hydrogen  and  incompletely  oxidized  carbon  composing  the  wood 
until  the  latter  has  been  entirely  transformed  into  carbon  dioxide 
water  and  inorganic  salts.  The  process  of  oxidation  is  therefore 
always  accompanied  with  the  liberation  of  energy.  We  may  say 
therefore  that  an  incompletely  oxidized  substance  contains  poten- 
tial energy  locked  up  within  itself.  Just  as  the  process  of  oxida- 
tion is  accompanied  with  the  liberation  of  energy  so  the  process 
of  reduction  can  only  take  place  at  the  expense  of  work.  No 
energy  can  be  created  anew  or  lost  in  the  world  and  therefore 
the  process  of  locking  up  of  potential  energy  within  the  compounds, 
in  the  present  case  the  sugar  and  the  starch  formed  by  the  chloro- 
phyll granules,  can  only  be  accomplished  by  the  supply  of  energy 
from  without.  Whence  then  comes  this  energy  from  without, 
enabling  the  chlorophyll  granules  to  tear  apart  the  oxygen  from 
the  COo  of  the  atmosphere  and  form  therefrom  sugar  and  starches 
capable  of  liberating  again  upon  oxidation  exactly  the  same  amount 
of  energy? 

It  comes  from  the  sun's  rays.     In  the  absence  of  these,  the 
cbloroplasts  cannot  form  sugar  from  the  carbon  dioxide,  and  we 

70 


THE  CHEMICAL  UNITS   OF  THE  BODY 

may  consider  the  sugar  and  starc^has  compounds  containing  locked 
up  -v^-ithin  themselves  the  energy  in  the  sun's  rays,  which  formed 
this  starch  and  sugar  from  the  CO2  of  the  atmosphere. 

The  Formation  of  Fats  from  Carbohydrates — By  means  of  the 
energy  supplied  by  the  oxidation  of  some  of  the  carbohydrates 
formed  in  the  manner  described  above,  a  portion  of  the  carbon 
is  still  further  deoxidized  to  the  form  of  fat.  Potential  energy 
may  therefore  be  stored  up  in  these  two  forms,  carbohydrates  or 
fats.  The  latter  stores  more  potential  energy  than  the  former, 
although  the  extra  portion  of  stored  energy  only  equals  that 
energy  lost  by  the  deoxidized  portion  of  the  carbohydrates.  The. 
formation  of  fats  from  carbohydrates  is  not  limited  to 
plants  alone.  Animals  also  possess  this  power.  The  relative 
amount  of  oxygen  contained  by  the  carbohydrates  and 
fats  and  therefore  the  greater  susceptibility  of  fats  to  oxidation 
is  well  illustrated  by  comparing  their  formulas,  CgHiaOg  (sugar) 
and  (C5iH9806)3  (tripalmatin).  It  is  readily  appreciated  by  this 
comparison  how  much  more  oxygen  the  fats  are  capable  of  com- 
bining with  and  therefore  how  much  more  energy  they  are  Capable 
of  liberating  for  use  by  the  body.  If  when  they  are  used  by  the 
body  for  the  production  of  energy  they  combine  as  they  do  with 
more  oxygen  than  the  carbohydrates  the  body  will  be  obliged  to 
breathe  in  more  oxygen  from  the  external  air  in  comparison  to 
the  amount  of  CO,  or  completely  oxidized  carbon  which  it  elimi- 
nates from  itself  than  when  the  body  is  burning  the  carbohydrates. 
When  therefore  fats  are  being  burned  in  the  body  the  fraction 
representing  the  CO,  exhaled  divided  by  the  0^  inhaled  will  be 

CO2  ""  .      ^ 

less.    This  fraction  -jr-   is  called  the  respiratory  quotient  and  is  of 
O2 

very  great  importance  in  investigating  the  changes  of  the  food- 
stuffs within  the  body  as  it  tells  us  just  how  much  of  this  one  or 
that  one  is  being  consumed. 

•The  Formation  of  the  Alcohol  Portion  of  a  Fat — In  the  first 
place  a  fat  is  a  combination  of  an  alcohol  and  a  fatty  acid.  In 
other  words,  an  ester. 

Almost  all  the  fats  formed  in  nature  are  compounds  of  glyeerol,-^ 
which  is  an  alcohol  of  three  methane  molecules  joined  together. 

This  portion  of  the  fat  is  easily  formed  from  either  glucose, 
fructose,  or  mannose.    The  first  .step  occurs  with  ease  by  the  simple 

72 


THE   CHEMICAL   UNITS   OF   THE   BODY 

exposure  of  the  solutions  of  th^  sugars  to  the  sunlight  according 
to  the  following  plan: 

CH2— oh;;~^^.^:^,c~— 

I  ^O^C>  .CH2OH 

CHOH  I 

I      "  CHOH 

OH  — C  — H  I  I 

I  +    OH  =  H  — C=rO +H2O 
H  — COH  I         / 

r,\    /iwrp^>s      I  H       '  CH^OH 

C^\^}M^^    CHOH  I 

I  CHOH 

COH  I 

H  — C  =  0 

The  new  substance,  of  which  two  molecules  are  thus  formed, 
is  called  glycerol  aldehyde.  This  aldehyde,  by  a  simple  reduction, 
becomes  glycerin,  the  addition  of  two  atoms  of  hydrogen  being 
all  that  is  necessary. 

The  Formation  of  the  Fatty  Acid  Portion  of  Fat — So  much  for 
the  glycerin  portion.  What  now  of  the  fatty  acid  portion?  Al- 
most all  the  fats  in  the  body  are  combinations  of  glycerol  and  either 
palmitic  acid  (CH3(CH2)i4.C00H)  or  stearic  acid  (CH3.(CH2)i6- 
COOH)  or  oleic  acid,  an  unsatisfied  fatty  acid  in  which  two  of 
the  carbon  atoms  are  united  together  by  a  double  bond  thus: 
CH2  =  CH.(CH2)i5COOH.  The -combination  with  glycerin  gives 
tripalmitin  or  tristearin  or  triolein  which  in  mixtures  of  various 
proportions  form  practically  all  the  fat  of  the  body.  The  fol- 
lowing reaction  illustrates  the  formation  of  tripalmitin: 


CH2O  H      HO  OC.(CH2)i„CH3 


CHO 


CH,0 


H4-HO 
H      HO 


OC,(CH2),„CH3r 

OC,(CH2),„CH3 

CH2OOC,(CH0a4,CH3 

I 
CH  OOC,(CH2)i4,CH3  -f  3H2O 


CH200C,(CH2)i4,CH3 
74 


THE   CHEMICAL   UNITS   OE   THE   BODY 

This  is  a  combination  which  both  plants  and  animals  can  easily 
accomplish  by  a  ferment  which  is  widely  distributed.  The  forma- 
tion, however,  of  the  fatty  acid  involves  changes  which  are  some- 
what more  intricate. 

The  Manner  in  which  the  Higher  Fatty  Acids  Are  Formed— 
We  have  seen  that  glycerol  aldehyde  could  be  easily  formed  from 
glucose,  and  that  if  the  aldehyde  is  reduced  glycerin  is  formed.  If 
instead  of  being  reduced  one  of  the  oxygen  atoms  is  shifted,  lactic 
acid  will  be  formed  thus : 

{Glycerol  aldehyde)  {Lactic  acid) 

CH,OH CH3 


CHOH 

1    , 
CHO  -^ 


CHOH 
COOH 


Lactic  acid  may  readily  break  apart  into  a  simpler  aldehyde 
and  formic  acid,  thus: 

{Acetic  aldehyde) 
CH3 

1      CH3   H 
CHOH  =\       +1 
I      CHO   COOH 
COOH 

Two  molecules  of  acetic  aldehyde  may  then  become  condensed 
into  adol. 

{Adol) 


rcH3 

1 

CHO 


CH3 


=  CHOH 

I 
CH2 

I 
CHO 


Then  by  a  shifting  of  the  H  and  OH  groups  in  precisely  the 
same  manner  as  lactic  acid  was  formed  from  glycerol  aldehyde,  a 

76 


THE   CHEMICAL   UNITS   OF   THE   BODY 

fatty  acid,  composed  of  two  more  methane  molecules  than  acetic 
aldehyde,  would  be  formed  thus: 


CH3 

H 

{Butyric  acid) 

CH3 

1 

H 

HO    CH 

CH, 

> 

' 

1 
CH2 

1 
OC 

CH2 

1 

OH 

H 

OH 

COOH 

It  is  significant  that  all  the  fatty  acids  occurring  in  nature 
possess  an  even  number  of  carbon  atoms,  as  if  each  one  with  a 
greater  number  of  methane  atoms  had  been  formed  in  the  manner 
above  outlined  by  an  increase  of  two  additional  methane  mole- 
cules at  a  time. 

The  Formation  of  Proteins — The  formation  of  the  remaining 
foodstuffs,  the  proteins,  is  still  more  intricate  and  little  more 
than  possibilities  about  the  processes  concerned  are  known.  Of 
all  three  classes  of  foodstuffs  we  may  consider  that  the  proteins 
are  most  important.  Living  protoplasm  can  only  be  formed  of 
protein,  so  that  while  the  energy  needs  of  the  body  can  be  sup- 
plied from  either  the  fats,  carbohydrates  or  proteins,  no  growth 
or  repair  of  a  living  cell  can  occur  without  proteins. 

The  Nitrogen  Contents  of  Proteins — The  most  distinguishing 
feature,  perhaps,  of  proteins  is  the  fact  that  they  contain  nitrogen. 
All  proteins  contain  the  following  elements : 

Carbon   50.6  —  54.5  per  cent. 

Hydrogen  6.5—   7.3    "  '' 

Nitrogen   15.0  —  17.6    *'  '' 

Sulphur    0.3—   2.2    "  " 

Oxygen   21.5  —  23.5    ''  " 

Nearly  all  proteins  contain  in  addition  phosphorus  0.4  to  0.8 
per  cent. 

The  Physical  Characteristics  of  Proteins — The  proteins  are 
amorphous,    indiffusiblC;   inert,   and   tasteless.      The  majority   of 


THE   CHEMICAL   UNITS   OF   THE   BODY 

them  are  soluble  in  water,  weak  salt  solutions  or  in  dilute  acids 
or  alkalis.  Many  of  them  are  precipitated  from  their  solutions 
by  the  simplest  physical  agents,  such  as  merely  shaking,  and  a 
very  large  number  are  precipitated  by  a  temperature  of  80°  C. 
The  white  of  egg,  egg  albumen,  is  a  typical  protein  and  presents 
all  the  characters  which  have  been  enumerated  above. 

Some  proteins,  hemoglobin  and  egg  albumen  may  be  crystallized, 
but  it  is  very  difficult  to  render  the  crystals  free  from  the  mother 
liquor,  and  hence  it  is  impossible  to  view  the  crystals  as  repre- 
senting the  same  chemical  and  physical  purity  as  is  the  case  of 
crystals  of  inorganic  salts. 

The  Size  of  the  Protein  Molecule — It  is  possible  to  arrive  at 
some  idea  of  the  minimum  size  of  the  protein  molecule  by  a  cal- 
culation based  on  the  relative  amount  of  that  element  which  is 
present  within  it  in  the  smallest  amount  and  contained  in  a  frag- 
ment or  portion  of  the  protein  molecule,  the  structure  of  which 
we  are  familiar  with. 

Thus  we-  know  that  all  the  sulphur  is  present  in  the  cystin 
portion  of  the  protein  molecule.  "We  know  the  formula  of  cystin 
and  that  it  contains  two  atoms  of  sulphur.  It  is  evident,  then, 
that  a  protein  containing  one  per  cent,  of  sulphur  could  not  have 
a  molecular  weight  of  less  than  3200.  In  the  same  manner,  using 
the  iron  in  the  hemoglobin  as  the  element  upon  which  to  base  our 
calculations,  oxyhemoglobin  cannot  have  a  molecular  weight  of 
less  than  11,200  to  14,000. 

In  some  instances  a  definite  depression  of  the  freezing  point, 
or  elevation  of  the  boiling  point  of  a  solution,  by  the  addition  of  a 
certain  percentage  of  protein  will  be  accompanied  by  a  definite 
increase  in  the  osmotic  pressure  of  the  solution.  This  fact  may  be 
made  the  basis  in  a  calculation  of  the  size  of  the  protein  molecule. 
Using  this  method,  a  molecular  weight  of  30,000  has  been  calculated 
for  serum  proteins  and  of  16,000  for  hemoglobin.  These  figures  cor- 
respond fairly  well  with  those  obtained  by  the  first  method  men- 
tioned. 

The  Different  Varieties  of  Proteins — The  following  are  the 
different  kinds  of  proteins  and  their  characteristics: 
1 . — Protamin  es .    ^ 

(a)  They  occur  only  in  combination  with  other  groups. 

(b)  They  contain  a  large  amount  of  bases  as  much  as  85  per 

80 


THE   CHEMICAL   UNITS   OF   THE   BODY 

cent,  of  the  total  substance  and  hence  form  well  marked 
salts  with  chlorides  or  sulphates. 

(c)  They  contain  no  sulphur. 

(d)  They  do  not  coagulate  with  heat. 

(e)  Soluble  in  water. 

(f)  They  will  precipitate  aqueous  solutions  of  other  proteins. 

(g)  They  yield  comparatively  few  amino  acids. 
2. — Hist  ones. 

/-^a)   Also  occur  only  in  combinations.     Their  two  most  impor- 
tant combinations  are  nuclein  and  hematin. 
-(b)   Contain  a  high  proportion  of  diamino-acids  and  bases. 

(c)  In  presence  of  salts  they  are  coagulated  by  heat  and  the 

coagulum  is  soluble  in  dilute  acids. 

(d)  From   aqueous   solutions  they   are   precipitated   by   am- 

monia and  soluble  in  excess  of  the  same. 

(e)  Soluble  in  water. 
k3. — Albumins. 

o^  -  (a)   Soluble  in  pure  water  and  coagulable  by  heat. 

"» (b)   Precipitated  by  complete  saturation  of  their  solutions  by 

ammonium  sulphate  or  zinc  sulphate. 
_^  (c)    Two  varieties,   egg  albumin  and  serum  albumin,   which 
possess  different  rotatory  powers  on  polarized  light. 
4. — Glohulins. 
4^/^\  ^  '(a)  Insoluble  in  pure  water. 

,^b)   Soluble  in  the  presence   of  certain  amounts   of  neutral 

salts. 
-r  (c)    They  are  precipitated  from  their  solutions  by  complete 
saturation  of  the  latter  with  magnesium  sulphate  or 
half  saturation  with  ammonium  sulphate. 
Examples  are: 

Crystallin,  a  protein  from  the  crystalline  lens  of  the  eye; 
Serum  Globulin,  or  paraglobulin,  from  the  blood  plasma ; 
Fibrinogen,  also  a  constituent  of  the  blood  plasma,  and 
Paramyosinogen,   a   constituent  of  muscle,   are   all   globulins. 
Many  other  globulins  are  found  in  the  seeds  of  plants.     Among 
these  are  edestins,  from  hemp  and  cotton  seeds;  zein,  from  maize; 
legumin,  from  beans;  gliadins  and  glutelins,  contained  in  many 
of  the  cereals. 

5. — Phosphoproteins — These  proteins  are  characterized  by  pos- 

82 


THE   CHEMICAL   UNITS   OF   THE   BODY 

sessing  phosphorus  as  an  integral  part  of  the  molecule.    The  phos- 
phoproteins  are: 

(a)  Insoluble  in  water. 

(b)  Easily  soluble  in  alkalis  and  ammonia. 

(c)  They  are  dissolved  by  hydrochloric  acid  and  pepsin. 

(d)  Their  alkalin  solutions  cannot  be  coagulated  by  heat. 
Representatives  of  the  phosphoproteins  are  casein  og en  of  milk, 

and  vitellin,  the  main  protein  in  the  yolk  of  eggs. 
-. — 6. — Nucleo-proteins — These  proteins  also  contain  phosphorus 
but  differ  from  the  phosphoproteins  in  not  giving  up  the  phos- 
phoric acid  on  treatment  with  a  caustic  alkali  and  in  containing 
the  purin  bases.  The  latter  is  contained  in  the  nucleic  acid  portion 
of  their  molecule. 

By  gastric  digestion  the  nucleoproteins  are  split  into  a  protein, 
which  becomes  further  transformed  into  .peptone,  and  another 
simpler  protein,  called  nuclein.  By  treatment  with  strong  acids 
the  nuclein  is  further  split  into  a  histpne  or  protamin  and  nucleic 
acid.  The  nucleo  proteins  are  soluble  in  water,  salt  solutions  and 
dilute  alkalis.  Among  the  products  of  disintegration  of  nucleic 
acid  are  two  substances,  both  of  which  are  derivatives  of  the  body 
called  purin.  Purin  must  be  regarded  as  a  combination  of  a 
pyrimidin  nucleus  and  an  iminazol  nucleus. 

N  — CH 

■       II        II 
Pyrimidin  is     HC       CH 

I  I  ■ 
N  =  CH 

Iminazol  is         HC  — NH\ 

II  CH 

HC  —  N/' 

"When  both  are  combined  purin  is  formed,  the  formula  for 
which  is: 

iN  =  «CH 

I  I 

mc     'c  —  Nw  \ 

II         II  CH^ 

3N  =  ^C    —   W/ 
84 


THE   CHEMICAL   UNITS   OF   THE   BODY 

By  oxidizing  various  groups  of  this  molecule  a  number  of 
important  substances  which  are  found  in  the  urine  may  be  ob- 
tained. Thus  uric  acid  is  the  oxidized  product  of  the  2,  6  and  8 
carbon  atom  of  purin.    Its  formula  is: 

HN  — CO 

II  ■  - 

0  =  0       C  —  NH\ 

I        II  CO 

HN  — C  — NH/ 

The  substances  xanthin,  hypoxanthin,  adenin  and  guanin  are 
similarly  made  by  the  oxidation  of  other  carbon  atoms  of  purin. 
All  these  substances  appear  in  the  urine  and  may  be  increased 
in  amount  when  certain  abnormal  chemical  changes  occur  in  the 
body. 

Besides  the  purin  bodies  many  of  the  nucleic  acids  yield  on 
disintegration  a  carbohydrate.  The  following  scheme  will  repre- 
sent the  composition  and  cleavage  products  of  a  nucleoprotein : 


'Acid  proteins,  histones  or  protamines. 


Nucleoprotein- 


Nuclein. 


.Nucleic  acid 


Phosphoric  acid 
Carbohydrate 
Purin  bases 
l-Pyrimidin  bases 


.Proteoses  and  peptones. 


7. — Glycoproteins — These  proteins  are  a  combination  of  a  pro- 
tein and  a  carbohydrate.  The  carbohydrate  generally  contains 
nitrogen  as  glucosamin  or  galactosamin.  The  glycoproteins  may 
be  divided  into  two  groups:     (1) — the  mucins;  (2) — the  mucoids. 

The  mucins  form  the  most  important  component  of  the  mucus 
secreted  by  the  various  mucous  membranes.  It  performs  impor- 
tant protective  functions.  By  prolonged  boiling  with  acids  mucin 
may  be  made  to  undergo  hydrolytic  changes  which  are  very  similar 
to  the  hydrolytic  products  obtainable  from  other  proteins.  There 
are  formed  acid  albumin,  albumoses  and  galactosamin. 

86 


THE   CHEMICAL   UNITS   OF   THE   BODY 

The  Mucoids — The  second  class  of  substances  belonging  to  the 
glycoproteins  are  the  mucoids.  They  may  be  obtained  from  vari- 
ous tissues,  such  as  tendon,  bone  and  cartilage,  by  treating  these 
tissues  with  weak  alkalis.  In  these  tissues  the  mucoids,  together 
with  the  albuminoids,  form  the  intercellular  substance.  They 
yield,  upon  proper  treatment  with  acids,  a  protein  and  a  polysac- 
charide which  contains  nitrogen  in  the  amino-acid  form. 

The  Albuminoids — The  albuminoids  also  are  constituents  of 
intercellular  tissue.  All  these  substances  are  extremely  insoluble 
and  hence  they  are  well  adapted  to  form  the  supporting  tissue  of 
the  body.  Their  indigestibility  makes  them  unavailable  for  nutri- 
tive purposes. 

Moreover,  they  either  do  not  possess  certain  groups  of  atoms 
which  aje  common  to  other  proteins  or  they  possess  an  excess  of 
other  groups,  or  they  possess  polypeptides  which  are  extremely 
resistant  to  the  action  of  the  digestive  ferments,  so  that  upon 
digestion  the  complete  number  of  chemical  units  resulting  from 
their  hydrolysis  are  either  present  in  very  small  quantities  or  lack 
certain  units  necessary  for  the  full  function  of  protein  foodstuffs. 

Collagen  is  the  most  important  albuminoid.  It  is  the  main 
constituent  of  the  intercellular  substance  of  white  fibrous  connec- 
tive tissue.  It  is  converted  into  gelatin  on  prolonged  boiling  with 
water.  Among  the  products  of  hydrolysis  of  collagen,  tryosin  and 
tryptophane  are  lacking. 

Elastin  is  another  albuminoid.  It  may  be  obtained  from  con- 
nective tissue  rich  in  yellow  elastic  fibers.  It  is  very  insoluble  and 
practically  indigestible  in  the  alimentary  canal. 

Keratin  and  Neurokeratin  are  albuminoids.  The  former  is 
extracted  from  the  horny  epithelium  of  the  nails,  hairs  and  super- 
ficial layers  of  the  skin,  the  latter  from  the  neuroglial  frame  work 
of  the  nervous  system.  Both  these  bodies  contain  much  sulphur 
in  the  form  of  cystin,  are  very  insoluble,  and  practically  indi- 
gestible. 

The  Chemical  Units  of  Protein — So  much  for  a  descriptive 
definition  of  the  class  of  bodies  grouped  under  the  name  of  pro- 
teins. As  has  been  said  we  know  far  less  of  the  processes  or  stages 
by  which  they  are  formed  than  we  do  of  the  natural  syntheses  of 
fats  or  carbohydrates.     A  preliminary  step  to  the  knowledge  of 

88 


THE   CHEMICAL   UNITS   OF   THE   BODY 

the  metabolism  of  proteins  is  an  acquaintance  with  the  chemical 
units  of  which  the  protein  molecule  consists. 

The  protein  molecule  may  be  taken  apart  by  hydrolysis  and 
yield,  as  a  result  of  this  process,  a  considerable  number  of  amino 
acids. 

An  amino-acid  is  an  organic  acid  in  which  the  ammonia  rad 
ical  in  the  form  of  NHo  replaces  some  H  atoms  in.  the  mother 
substance,   other  than  that  of  the  acid  radical.     The   following 
are  the  amino-acids  which  proteins  yield  on  hydrolysis.     Their 
structure  illustrates  the  formation  of  an  amino-acid. 

H 

I 
Glycin,  or  amino-acetic  acid,  li  — ■  C  —  NH, 

I 
0=C— 0— H 

H 

I 
Alanin,  or  amino-propionic  acid,     H  —  C  —  H 

I 
H  —  C  —  NH, 

0=C— 0— H 
H 

Serin,  or  amino-oxypropionic  acid,    H  —  C  —  OIJ 

I 
H  —  C  —  NH;, 

I 
0  =  C  — OH 

CH3      CH3 

\/ 
CH 
Amino-valerianic  acid,  | 

H  — C  — NH2 

I 
0=0— 0—H 
90 


THE   CHEMICAL   UNITS   OP   THE   BODY 

CHg  CH3 

CH 

Leucin  or  dimetliyl-amino-butyric  acid  CH2 

or  amino- isobutyl- acetic,  | 

H  — C  — NH, 

I 
0  =  C  —  OH 

Isoleucin,   or   a-amino-mettiyl-ethyl-propionic   acid. 
Two  dibasic  acids  compounds  containing  a  double  acid  radical 
have  been  derived  from  proteins.     One  of  these  is  aspartic  acid. 

It  is  0  =  C  —  OH 

I 
H  —  C  —  NH2 

I 
H  — C  — H 

I 
0  =  C  —  OH 

The  second  is  glutamic  acid: 

It  is  0  =  C  —  OH 

I 

I 
H  — C  — H 

I 
H  — C  — H 

I 
0  =.C  —  OH 

A  number  of  compounds  containing  two  ammonia  groups  are 
obtained  from  the  protein  molecule.  These  are  called  the  diamino- 
acids.  The  first  one  is  lysin.  It  is  a-e-diamino-caproic  acid.  Its 
formula  is: 

92 


THE   CHEMICAL   UNITS   OF   THE   BODY 

H 

I 
H  — C  — NH2 

I 
(CH,)3 

I 
H  — C  — NH2 

I 
0=0— 0—H 

A  second  diamino-acid  is  ornithin.  It  is  diamino-valerianic  acid. 
Its  formula  is: 

H2ONH2 

I 
(OH,), 

I 
HONH2 

■  I 

0  =  0  —  OH 

A    combination   of   ornithin  with   urea   forms   arginin.      The 
formula  of  urea  is: 

H,N 


Arginin  therefore  is 


0  =  0 

/ 

H,N 

!  is: 

HN 

H 

\ 

1 

0  — N- 

-OH, 

/ 

1 

3,N 

(OHJ, 
1 

H- 

-0  — NH, 

0=^0  — 0—H 

Creatin  is  one  of  the  most  abundant  nitrogenous  extractives 
of  muscle.  It  has  a  formula  very  similar  to  arginin,  being  a 
combination  of  urea  and  methyl  glycin. 

94 


THE   CHEMICAL    UNITS   OF   THE   BODY 

Its  formula  is: 

HN  =  C  — NCCHg) 

I  1 

I 
0=C— 0— H 

Still  another  diamino  acid  is  diamino-trioxydodecoic  acid.  Its 
formula  is  indicated  by  its  name  but  its  exact  structure  is  not 
known. 

The  remaining  known  amino-acids  composing  the  protein  mole- 
cule contain  the  benzene  group.  One  of  the  most  important  of 
them  is  ty rosin.  It  is  para  oxyphenyl  (a)  alanine  and  has  the 
formula :  ^t, 

/        \ 

\       /H      0 

1         I        II 
H,C  — C  — C  — OH 

I 
NH, 

Tyrosin  is  one  of  the  first  of  the  amino-acids  to  be  split  off 
from  the  protein  molecule.  Phenyl  {a)  alanin  is  very  closely 
related  to  tyrosin,  having  the  same  formula  minus  the  hydroxyl 
group.    It  is  an  almost  constant  constituent  of  proteins. 

Tryptophane  is  a  second  important  amino-acid  compound  of 
the  benzene  series.  It  is  indol-amino-propionic  acid.  Its  for- 
mula is: 

H 

C  H,    H      0 

/     \  II        I        II 

H  — C  C c  — C  — C  — C  — 0  — H 

I  I  I  I 

H  — C  C  CH  NHj, 

\      /      \        / 
C  NH 

I 
H 

96 


THE   CHEMICAL   UNITS   OF   THE   BODY 

The  relation  of  indol 

—  C.H  C  —  CH3 

CgH^  \and  skatol  GJl^  \\ 

—  N  — C.H  — N  — C  — H 

H  I 

H 

the  two  substances  responsible  for  the  odor  in  the  feces,  to  trypto- 
phane is  of  much  interest,  as  is  also  the  relation  of  all  three  sub- 
stances to  Indican 

0 

—  C S  — C  — H 

CeH,  II  II 

—  N  — C.H       0 

I 
H 

which  is  the  form  in  which  the  ethereal  or  conjugated  sulphur 
appears  in  the  urine. 

Tryptophane  and  tyrosin  are  responsible  for  the  characteristic 
reaction  which  proteins  give  with  Millon's  reagent.  They  are 
absent  from  the  albuminoids,  collagen,  gellatin,  elastin,  etc.,  hence 
these  bodies  do  not  give  the  protein  test  with  Millon's  reagent. 

Prolin,  Oxyprolin  and  Histidin — By  the  closing  of  an  open 
chain  of  a  simple  amino- acid  it  is  possible  to  obtain  the  so-called 
heterocyclic  compounds,  such  as  those  represented  by  the  three 
bodies,  prolin,  oxyprolin  and  histidin.  Thus  by  closing  up  the 
open  chain  compound,  oxy-amino-valerianic-acid, 

H-2     H2     Hg     H     0 

II        II        II         I        II 
H— 0— C— C— C— C— C— 0— H 

I 
NH2 

and  at  the  same  time  dehydrating,  a  compound  identical  with 
prolin  is  formed.  In  it  the  NH  group  become  united  with  both 
the  a  and  8  carbon  atom.    It  has  the  formula : 

98 


THE   CHEMICAL   UNITS   OF   THE   BODY 


Hg   H2 


C  — C  0 

/  \         II 

H,  —  C  c  —  C  —  OH 


H 


N 


H 

The  third  body,  histidin,  is  a  combination  of  a  -amino-pro- 
pionic acid  and  iminazol.  Iminazol  may  be  regarded  as  a  closed  ring 
formed  by  the  combination  of  two  simple  amino-acids,  united  by 
their  ammonia  groups,  the  ammonia  group  of  each  amino-aeid  unit- 
ing with  the  carbon  atom  of  the  earboxyl  group  of  the  other  amino- 
acid  which  becomes  at  the  same  time  completely  deoxidized,  thus : 


H2    H2 

II       II 
C— N.     0 

II 
+  C  -  OH  = 

I 
.COOH   NH2 

Histidin  is 

H      H 


H     H 


C  — N. 


C  — N 

I 
H 


\ 
( 


C  — H 


C  — N 


C 


\ 


c- 

II 

H, 


N 
H 

I 
-C 


CH 


/ 


O 


C  — OH 


NH2 
100 


THE  CHEMICAL  UNITS   OF  THE  BODY 

Cystin — The  fourth,  group  of  bodies  which  form  an  important 
part  of  the  protein  molecule  contain  sulphur.  Practically  all  of 
the  sulphur  in  protein  is  contained  in  the  group  known  as  cystin. 
Cystin  may  be  viewed  as  a  combination  of  two  cystein  molecules. 
The  cystein  molecule  is  simply  a  molecule  of  oxy-amino-pro- 
pionic  acid,  in  which  the  sulphur  takes  the  place  of  the  oxygen 
atom  of  the  hydroxyl  group.     It  has  the  formula: 

H3 

C  — S  — H 

1 
H  — C  — N^H, 

C  =  0 

I 

0  — H 

Its  chemical  name  is  a-amino-thiopropionic  acid.  Cystin  itself 
has  the  formula: 

II  II 

c_s  —  s  —  c 

I  I 

H  — C  — NH2   H2N  — C  — H 

I  I 

c  =  o  c  =  o 

I  I 

0_H  0— H 

Glucosamin  and  Its  Significance — The  protein  molecule  eon- 
tains  other  bodies  besides  the  above  previously  mentioned  amino- 
acids.     Only  one  of  these  other  possible  components  of  protein 
has  been  isolated.    It  is  glucosamin.    It  has  the  formula : 
H,  — C  — 0  — H 


(H  — C- 

1 

-0  — H) 

1 
H  — C- 

1 

-  NH2 

1 
H  — C  = 

-0 

102 

V 


THE   CHEMICAL   UNITS   OF   THE   BODY 

This  body  is  of  considerable  interest  because  it  illustrates  the 
possibilities  of  passing  from  a  carbohydrate  to  an  amino-acid. 
Serin,  or  oxy-amino-propionic  acid,  is  the  simplest  member  of  the 
type  of  bodies  to  which  glucosamin  belongs. 

The  Polypeptids  and  the  Manner  in  Which  They  Are  Formed 
— The  various  possibilities  by  which  these  various  amino-acids  and 
their  derivatives  may  be  united  together  in  the  protein  molecule 
are  of  much  interest  as  it  indicates  something  about  the  manner 
in  which  the  protein  molecule  is  formed,  and  also  how  it  may  be 
built  up.  Fischer  has  actually  combined  together  as  many  as 
eighteen  of  the  various  amino-acids,  including  even  such  bodies  as 
cystin.  In  such  combinations  he  has  shown  that  the  various  mem- 
bers are  united  by  the  NH  and  CO  groups. 

Thus  two  molecules  of  leucin  may  be  united  thus : 

CH3  CHg 

\  / 

CH 

I 

I 
C  — H 

/  \ 
H— N  C=0 

I  I 

0  =  C  N  — H 

\  / 
C  — H 

I 

I 

C  — H 

/  \ 

CH3  CHg 

Combinations  of  this  character  are  called  polypeptids. 

Polypeptids  are  found  among  the  products  of  protein  digestion. 
They  resemble  in  all  respects  peptones.  They  are  soluble,  dif- 
fusible, and  bitter.      The  higher  members  even  give  the  biuret 

104 


THE   CHEMICAL  UNITS   OF  THE  BODY 

reaction.  The  nitrogen  always  acts  as  the  connecting  element, 
but  it  may  unite  various  groups  in  a  rather  indefinite  number 
of  ways. 

Thus  four  structural  formulas  are  possible  f©r  glycyl  glyein. 
They  are: 

H2    H2     0      H      H2     0 

II       11       II        I        II       II 
N_C  —  C  —  N  —  C  —  C  —  OH 

or  H      H2     0 

I        II        II 

N  — C  — C 

/                    \ 
/  0 

0=0 C— N 


H2    H3 

or  H2     H2     OH  H2 

I         II         I  I 

N— C— C=N— C— C=0 

OH 
H2    0 

II       II 
N C  — C 

"  \ 

o 

/ 

C C  — N 

I  II       III 

OH      H2     H3 

The  Possible  Sources  of  the  Amino-Acids — From  the  preceding 
description  of  the  constitution  of  proteins  it  is  clear  that  their 
most  important  constituents  are  the  amino-acids.  The  most  im- 
portant factor,  therefore,  in  their  organic  synthesis  may  be  con- 
sidered to  be  the  formation  of  the  amino-acids  themselves.  Once 
these  components,  or  chemical  units,  are  formed  we  are  able  to 

106 


THE   CHEMICAL   UNITS   OF   THE   BODY 

pass  by  easy  transition  to  the  polypeptids,  which  are  simply 
combinations  of  the  amino-acids.  Having  accounted  for  the  forma- 
tion of  the  polypeptids  we  have  followed  many  of  the  steps  in- 
volved in  the  synthesis  of  proteins :  for  the  polypeptids  are  closely 
related  to  peptones.  The  peptones  may  be  considered  among  the 
primary  hydrolytic  products  of  proteins.  The  actual  steps  in- 
volved in  the  formation  of  the  varioiis  amino-acids  are  not  known, 
but  the  formation  of  amino-propionic  acid  from  lactic  acid  illus- 
trates the  possibility  of  the  formation  of  this  amino-acid,  an  amino- 
acid  which,  at  least,  may  be  considered  one  of  the  most  important 
ones,  from  carbohydrates.  We  may  consider  that  the  steps  in- 
volved are  probably  the  ones  concerned  in  the  formation  of  this 
fundamental  chemical  unit  of  proteins. 

We  have  already  shown  how  lactic  acid  may  be  formed  from 
glucose.  This  is  a  change  which  readily  occurs  under  simply 
the  catalytic  influence  of  alkaline  calcium  hydrate.  Lactic  acid 
is  easily  formed  from  not  only  glucose,  but  also  from  fructose  and 
mannose,  by  many  microorganisms.  It  seems,  however,  to  be 
formed  with  considerable  difficulty  from  galactose.  The  formula 
for  lactic  acid  is: 

CH3 

I 
HC  — OH 

I 
0  =  0 

I 

0  — H 

Lactic  acid  in  the  presence  of  ammonia  and  some  dehydrating 
agent  will  give  amino-propionic  acid  thus : 

{Lactic  acid)  {Amino-propionic  acid) 

CH3  CH3 

1  i 

H  —  0  —  OH  +  NH3  :=  H  —  C  —  NH2  +  H2O 

I  •  I 

0=0  0=0 

I  I 

0  — H  0  — H 

108 


THE   CHEMICAL   UNITS   OF   THE   BODY 

The  formation  of  amino-propionic-  acid  from  lactic  acid  is 
not  the  only  method  of  transition  from  carbohydrates  to 
amino-acids  which  is  possible.  "We  have  seen  that  certain  inter- 
mediate products  and  certain  by-products  are  produced  in  the 
formation  of  sugar  and  starch  from  carbon  dioxide.  One  of  the 
intermediate  products  in  the  synthesis  of  starch  is  glyoxylic  acid, 
a  keto  acid, 

H  — 0  =  0 

I 

c  =  o 

I 

0  — H 

This  substance,  plus  NHg,  will  yield  glycin,  or  amino-acetic- 
acid.  In  general,  it  may  be  said  that  the  amino-acids  are  formed 
by  the  production  first  of  the  a-oxy-acids,  which  react  with  am- 
monia to  produce  the  amino-acids  of  the  protein  molecule. 


no 


QUESTIONS  AND  ANSWERS 


Page  2 
Q.  What  are  the  structural  units  of  the  body? 
A.  The  cells  of  the  body. 

Page  6 
f/    Q.  Define  protoplasm. 

A.  Protoplasm  is  a  collection  of  organic  compounds  of  varied  chemical 
structure,   the   essential    members   of   which   are    proteins   which   together    are 
capable  of  performing  vital  activities. 
\J  ^.  Describe  a  cell. 

A.  S^e  1,  2,  3,  and  4  under  * '  The  structure  of  a  cell. ' ' 

1 ,  \      Page  12 

v^'Q.  What  are  the  functions  of  the  plasmahaut? 
A.  1.    It  preserves  the  form  of  the  cell. 

2.    It  controls  the  passage  of  soluble  substance  to  and  from  the  cell. 

Page  14 
\  "l^  Q.  What  are  the  vital  phenomena  of  cells? 
■\A-  See  1,  2,  3,  4,  5,  6,  7  and  8. 
Ar     Q.  What  is  assimilation? 

A.  Assimilation   is  those  processes  by   which   cells  appropriate   the  sub- 
stances of  use  to  them  in  the  exercise  of  their  vital  activities; 
^KQ.  What  is  dissimilation? 

A.  Dissimilation  is  those  processes  by  which  cells  utilize   the  assimilated 
products  iu  the  exercise  of  their  vital  activities. 

Page  16 
/ Q.'What  is  excitability? 

A.  Excitability  is  that  property  of  living  cells  which  enable  them  to   re- 
spond to  stimuli. 

Q.  What  is  contractility? 

A.  Contractility  is  that  property   of   living  cells  which   enables  them   to 
shorten  one  of  their  diameters. 

V^.  What  is  adaptability? 

A.  Adaptability  is  that  property  of  living  cells  by  which  they  undergo  an 
internal  adjustment  to  external  environment. 

^Q.  What  is  growth? 

A.  Growth  is  that   property* of  living  cells  by   which   they  interruptedly 
increase  in  size. 

112 


y: 


dyi'i' 


iitMM.Q/vxy         '■.j&IdJ&^ 


QUESTIONS  AND  ANSWEES 

/  Page  18 

■/  Q.  Describe  cell  division  by  amitosis. 

A.  See  text. 
v/  Q.  Describe  cell  division  by  karyokinesis. 

A.  See  text. 

J  Page  26 

'   Q.  What  is  conduction? 

A.  Conduction  is   the  property   of  cells  which  enables  them  to  transmit 
stimuli. 


V. 


Page  28 

Q.  What  are  the  functions  of  the  nucleus? 

A.  1,  The   nucleus   initiates  the   renewal   of   the  potential   forces   of    all 
the  vital  activities  of  cell  life. 

2.    It  "^ initiates  reproduction  and   determines  the  exact  characters  of  the 
reproduced    cells.     It  might  be  called  the  primer   and  organ  of  inheritance 
of  the  cell. 
vj  Q.  What  is  the  function  of  the  cytoplasm? 

"*  A.  The  cytoplasm  is  the  organ  ultimately  or  immediately  responsible  for 
those  changes  which  are  manifest  as  the  vital  activities  of  cell  life.  It  might 
be  called  the  agent  of  cell  activity. 


>^        'X^(P(^«,V  Fogeys  ^'''c'llrV 

//       VQ.  What  are  the  elements  composing  the  body?  ^       i3*\!^^^ 

Jl, I   A.  See  text.  >  \   \ 


I   A.  See  text.  ^^  \    \ 

J    Q.  What  is  the  ultimate  source  of  carbon  to  aU  life?        ^<^'  U 

A.  The  carbon  dioxid  of  the  atmosphere. 


^ 


Page  40 

In  what  form  is  the  carbon  made  available  to  life? 
A.  As  the  incompletely  oxidized  carbohydrates  and  the  still  more  incom- 


pletely oxidized  fats.  -  t.,^(^/^|^||  ^  ,  Q^  ^/^\ 

.  ■  Q.  In  what  form  is  carbon  eliminated  1  '-  b    lO  s 

A.  As  the  completely  oxidized  carbon  dioxid. 

Page  42 

Q.  How  is  hydrogen  assimilated  by  life? 
A.  As  water. 

;Q.  How  is  oxygen  assimilated  by  life? 
'a.  In  the  free  state  by  the  process  of  respiration. 
Q.  How  is  nitrogen  assimilated  by  plant  life? 

A.  1.  Chiefly  as  nitrates  formed  for^lant  life  by  electrical  disturbances 
from  the  nitrogen  of  the  air. 

2.  By  the  action  of  special  bacteria  from  the  nitrogen  of  the  air,  some 
of  which  bacteria  perform  their  nitrifying  aptivity  in  symbiosis  on  the  roots 
of  leguminous  plants. 

3.  From  decaying  organic  matter. 

114 


QUESTIONS  AND  ANSWEES 

Page  46 

Q.  How  is  sulphur  assimilated  by  plants? 

A.  As  the  sulphates^ 

Q.  How  is  sulphur  assimilated  by  animals  ?v 

A.  As  proteinsu 

Q.  How  is  phosphorus  assimilated  by  plants? 

A.  As  phosphates. 

Q.  How  is  phosphorus  assimilated  by  animal  lif©^  jW.  '"     ^  i        ^j     ' 

A.  As  phosphorus  in  organic  combination.  "    •''•''^^        ''^   «  ♦'"•t-c-t^j^AA^ 

Q.  How  is  iron  assimilated  and  what  is  its  function  in  the  body? 

A.  Iron  may  be  assimilated  as  organic  or  inorganic  iron,  and  is  an  essen- 
tial component  of  chlorophyll  and  hemoglobin,  substances  identified  with  im- 
portant respiratory  functions  in  plants  and  animals. 

\       ^-'' 

Page  48 

Q.  What  are  the  chemical  units  of  the  foodstuffs  of  plants? 

A.  The  twelve  elements  composing  their  tissues. 

Q.  What  are  the  chemical  units  of  the  foodstuffs  of  animals? 

A.  Combinations  of  the  twelve  elements  which  form  the  smallest  atom 
groups  from  which  the  animal,  by  synthetic  processes,  may  construct  its  pro- 
teins, fats  and  carbohydrates. 

Q.  Why  is  carbon  the  most  fundamental  element  of  life? 

A.  Because  its  peculiar  combining  powers  make  it  possible  for  the  forces 
available  to  vital  processes  to  form  that  endless  variety  of  compounds  from  it 
by  which  cells  can  perform   their   functions. 

Page  50 

Q.  What  are  the  mother  substances  of  all  the  organic  compounds? 

A.  Methane  and  benzene.     For  formulas  see  text. 

Q.  How  may  other  organic  compounds  be  formed  from  these  two  mother 
substances? 

A.  By   replacing   one   or  more   of   the   hydrogen   atoms  with   other    atom 
groups,  including  among  these  other  atom  groups  the  mother  substances  them- 
selves. 
■s^Q.  Illustrate  these  compound  forms. 

A.  By  formulas  in  text. 
^^  Page  52 

Q.  What  is  an  alcohol? 

A.  An  addition  compound  formed  by  the  insertion  of  an  hydroxyl  group. 
See  text  for  illustration. 

Q.  What  is  an  aldehyde? 

A.  An  addition  compound  formed  by  the  insertion  of  an  atom  of  oxygen. 
See  text  for  illustration. 

Page  54 

Q.  What  are  the  characteristics  of  the  aldehydes? 
A.  1.    They  are  strong  reducing  agents. 
2.    They  easily  form  addition  products. 

116 


^,-t,+  fvH!^0'.^ii^^ii(^)j 


<XH 


>  'K  "Pa/  ^ 


tv-W 


-v>r. 


4        <? 


*-  ^fH 


-"4 


U.\^ 


yf-  q.K 


QUESTIONS  AND  ANSWERS 

3.    They  possess  strong  tendency  to  polymerize. 
See  text  for  illustration. 
Q.  What  is  an  organic  acid? 

A.  An  addition  product  formed  by  the  insertion  of  both  an  hydroxyl 
group  and  an  atom  of  oxygen  to  the  sa^e  carbon  atom,  ^ee  text  for  illus- 
tration. '— ^ 

Page  58 

Q.  What  is  an  oxyacid? 

A.  An  addition  product  formed  by  the  insertion  of  a  hydroxyl  group 
into  an  organic  acid.    See  text  for  illustration. 

Q.  What  is  a  keto  acid? 

A.  An  addition  product  formed  by  the  insertion  of  an  ato|»  6f  oxygen 
into  an  organic  acid.     See  text  for  illustration.  ^     «^ 

Q.  How  are  the  unsatisfied  series  of  carbon  compounds  foriopd? 

A,  By  the  union  of  adjacent  cgjjral  carbon  atoms  of  compound  forms 
by  more  than  one   bond.     See  text  for  illustration. 

Q.  How  are  the  compound  forms  of  the  benzene  series  formed?  ~~ 

A.  By  the  same  principles  given  for  the  formation  of  the  compounds 
of  the   methane  series.     See  text  for  illustration. 

Page  64 

Q.  What  are  the  first  successive  substances  :^(:!rmed  by  tli«l  processes  in- 
J^lved  in  the  assimilation  of  carbon  by  the  plant,  and  what  progressive 
changes  in  the  chemical  condition  of  the  carbon  do  these  substances  represent? 

A.  1.    Formaldehyde  and  a  by-product,  hydrogen  peroxid. 

2.    Polymerization  of  formaldehyde  into  a  hexose  and  the  destruction 
of  the  hydrogen  peroxid  by  catalase. 

These  products  represent  stages  in  the  deoxidation  of  carbon  as  it  occurs 
in  the  atmosphere. 

Q.  What  are  the  four  hexoses  and  the  principle  upon  which  the  difference 
between   them   depends? 

A.  1.  Glucose,  mannose,  fructose  and  galactose.  f  \ 

2.    The   difference  in  the  symmetry   of  the  position  of  the   hydroxyl 
and  hydrogen  atoms  attached  to  the  four  central  carbon  atoms. 

V 

I  Page  68 

\    Q.  What  are  the  disaceharides  of  physiological  importance  and  how  are 
they  formed? 

A.  1.    Maltose,  lactose  and  saccharose. 

2.    By  the  combination  of  two  of  the  simple  hexoses  with  the  loss  of  a 
molecule  of  water.  y. 

They  represent  therefore  a  second  stage  in  the  deoxidation  of  the  carboiJ-'^^ 
assimilated  by  the  plant. 

Q.  What  is  starch  and  what  does  it  represent? 

A.  A  polysaccharide  with  the  loss  of  probably  some  58  molecules  of  water. 
It  represents  a  more  advanced  stage  of  deoxidation  of  the  assimilated  carbon. 

118 


QUESTIONS  AND  ANSWEBS 

Fage  70 

Q.  What  is  the  function  served  by  the  formation  of  incompletely  oxidized 
forms  of  carbon? 

A.  The  creation  of  substances  possessing  potential  energy. 

Q.  Whence  comes  the  energy  for  the  creation  of  potential  energy  in  the 
plants? 

A.  From  the  sun's  rays. 

Page  72 

*      Q.  Ho-n"  are  the  fats  formed  by  the  plants  and  animals? 

A.  By  the  reduction  of  the  carbohydrates,  the  energy  being  supplied  by 
the  oxidation  of  other  carbohydrates. 

Q.  Do  fats  represent  an  increase  in  the  energy  stored  by  the  plant? 

A.  In  one  sense  no,  because  although  fats  contain  more  potential  energy 
than  plants,  they  store  this  gi-eater  quantity  at  the  expense  of  energy  already 
stored  in  the  carbohydrates  of  the  plant. 

Q.  What  is  a  fat? 

A.  A  combination  of  an  alcohol  and  a  fatty  acid.    )^  o^w  ht^^C'' 

^  -  ■     -•  -r  - 

Fage  74 

\j       Q.  What  are  the  three  most  abundant  fats  in  the  body? 
*         A.  Triolein,  tripalmitin,  tristearin,  all  combinations  of  glycerin  and  three 
molecules  of  a  relatively  high  fatty  acid. 

Fage  78 

Q.  What  is   the   distinguishing  characteristic  of   protein   as  a   foodstuff? 
A.  It  contains  nitrogen,  and  is  alone  able  to  rebuild  the  ceU. 
Q.  What  are   the   characteristic   elements  of  proteins  and   their   approxi- 
mate percentages? 
A.  Carbon  50%. 

Hydrogen  6%. 

Nitrogen  15%.-««. 

Sulphur  1%. 

Oxygen  20%. 
■    ^ttrv*^  -^70  Fages  80-86 

Q.  What  are  the  phj:sieal  characters  of  proteins? 

A.  See  text.  .\.- 

Q.  What  are  the  different  kinds  of  proteins  ana  some  of  their  distinguish- 
ing features? 

A.  1.  Protamines  are  compound  proteins,  yielding  few  amino  acids,  but 
contain  a  large  amount  of  bases. 

2.  Histones  are  compound  substances  represented  by  hematin  and  nuclein, 
and  contain  large  amount  of  bases  and  diamino  acids. 

3.  Albumins,  soluble  in  water,  coagulable  by  heat,  and  precipitated  by 
complete  saturation  with  ammonium  or  zinc  sulphate. 

4.  Globulins,  insoluble  in  water,  precipitated  from  solutions  by  half  satu- 
ration with  ammonium  sulphate. 

5.  Phosphoprotoins  contain  a  large  amount  of  phosphorus  in  special  com- 

120 


\iL  i\ 


QUESTIONS  AND  ANSWEES 

bination  which  they  yield  on  treatment  with  caustic  a      li.     Insoluble  in  water, 
but  dissolved  by  hydrochloric  acid  and  pepsin. 

6.  Nucleoproteins  also  contain  phosphorus  in  special  combination  which  is 
not  given  up  by  treatment  with  caustic  alkali.  Soluble  in  water,  split  by 
gastric  digestion  into  insoluble  nuclein,  which  in  turn  yields  phosphoric  acid, 
a  purin  base  and  a  carbohydrate. 

7.  Glycoproteins  are  a  combination  of  proteins  and  a  carbohydrate-like 
body.     The  mucins  and  mucoids  are  glycoproteins. 

Page  88 

Q.  What  are  the  albuminoids? 

A.  Substances  resembling  proteins,  but  extremely  insoluble  and  indigestible 
and  lacking  certain  atom  groups,  as  the  tryptophane  group,  which  is  present 
in  true  proteins.v  They  are  collagen,  from  the  intercellular  tissue  of  white 
fibrous  tissue;  elastin,  from  the  yellow  elastic  tissue;  and  keratin,  from  the 
nails  and  hair. 

V  Page  90 

Q.  /What  are  the  known  chemical  units  of  proteins'? 


^  ^^y'l,  Glycin,  or  amino-acetic  acid,  with  formula.     ^ 

"S    •*    2.  Alanin,  or  amino-propionic  acid,  with  formula.  . 

^-    i  3.  Serin,  or  amino-oxypropionic  acid,  with  formula.    eji>-^'^^^*^^^  +!i^  fi^' •> 

^  4.  Two  dibasic  acids,  with  an  illustration  of  one.  ""»    0-"*^*^^        ^^\ 

6/5.  A  diamine  acid,  lysin,  and  definition  of  a  diamino  acid.      > 

^yp.  Creatin  and  knowledge  of  its  general  chemical  structure 

gl.  Tyrosin,  with  formula.  /         — ^ 

r.     .'..J^.  Tryptophane,  with  formula.  K~y  <C^-^,^ 

\J      1 9.  Grlycosamin   and  formula 

yio.  '     ' 


K. 


Cystin,  with  formula. 

Fage  104 


Q.  What  is  a  polypetid? 

A.  A  polypeptid  is  a   combination   of  varying  numbers  of  amino   acids 
united  by  their  contiguous  NH  and  CO  groups. 

Tage  106 

Q.  What  is  the  source  of  amino  acids  in  the  animal  body? 
A.  Chiefly  by  the  hydrolysis  of  proteins,  but  to  a  limited  extent  by  syn- 
thesis.    It  is  possible  that  both  glycin  and  alanin  may  thus  be  formed. 


122 


COLUMBIA  UNIVERSITY  LIBRARIES 

This  book  is  due  on  the  date  indicated  below,  or  at  the 
expiration  of  a  definite  period  after  the  date  of  borrowing, 
as  provided  by  the  library  rules  or  by  special  arrangement 
with  the  Librarian  in  charge. 

DATE  BORROWED 

DATE  DUE 

DATE  BORROWED 

DATE  DUE 

i 

1 

i 

C23    (1204)    BOM 

QP34 

J25 

1915 
Janeway  ^^^^^ 

Lecture  notes  on  physiology. 


OCT  i     1965  31NDERY 


